gh-39305: fixing some ruff PLR warnings
    
here about useless return at the end of functions and methods

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #39305
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/algebras/hecke_algebras/cubic_hecke_algebra.py

@@ -1116,7 +1116,6 @@ def check_base_ring_embedding(base_ring_embedding):
         # initializing the basis extension (in case of more than 4 strands)
         # ----------------------------------------------------------------------
         self._init_basis_extension()
-        return
 
     ############################################################################
     # --------------------------------------------------------------------------

src/sage/algebras/hecke_algebras/cubic_hecke_base_ring.py

@@ -105,8 +105,6 @@ def register_ring_hom(ring_hom):
         except ValueError:
             verbose('\nthe map:\n%s\ncannot be registered as conversion\n' % ring_hom)
 
-    return
-
 
 # -----------------------------------------------------------------------------
 # class for the Galois Group action on the generic extension ring corresponding
@@ -1005,11 +1003,10 @@ def __init__(self, names=('u', 'v', 'w', 's'), order='degrevlex', markov_trace_v
         # Init of data used on demand
         # ----------------------------------------------------------------------
         self._mirror = None
-        return
 
-    ############################################################################
+    # ########################################################################
     # overloaded inherited methods
-    ############################################################################
+    # ########################################################################
     def _defining_names(self):
         r"""
         Return the generators of ``self`` as the defining names.

src/sage/categories/affine_weyl_groups.py

@@ -130,7 +130,7 @@ def succ(pair):
                     if (length < k and i == u1.first_descent(side='left') and
                             u1.is_affine_grassmannian()):
                         yield (u1, length + 1)
-                return
+
             return RecursivelyEnumeratedSet_forest(((self.one(), 0),), succ, algorithm='breadth',
                                                    category=FiniteEnumeratedSets(),
                                                    post_process=select_length)

src/sage/combinat/diagram_algebras.py

@@ -4795,7 +4795,7 @@ def insert_pairing(cur, intervals):
                 # Singleton intervals are vertical lines,
                 #   so we don't need to worry about them
                 if len(I) > 1 and I[0] < cur[0]:
-                    cur, level[j] = level[j], cur
+                    cur, level[j] = I, cur
                     level.append([cur[0]])
                     level.append([cur[1]])
                     break

src/sage/combinat/necklace.py

@@ -360,12 +360,11 @@ def _fast_fixed_content(a, content, t, p, k, r, s, dll, equality=False):
             content[j] += 1
             j = dll.next(j)
         a[t - 1] = k - 1
-    return
 
 
-################################
-# List Fixed Content Algorithm #
-################################
+# ###############################
+# List Fixed Content Algorithm  #
+# ###############################
 def _lfc(content, equality=False):
     """
     EXAMPLES::

src/sage/combinat/non_decreasing_parking_function.py

@@ -629,6 +629,5 @@ def iterator_rec(n):
             return
         for res in iterator_rec(self.n):
             yield NonDecreasingParkingFunction(res)
-        return
 
     Element = NonDecreasingParkingFunction

src/sage/combinat/tableau.py

@@ -8133,8 +8133,6 @@ def __iter__(self):
 
             yield self.element_class(self, tableau)
 
-        return
-
     def list(self):
         r"""
         Return a list of the standard Young tableaux of the specified shape.

src/sage/combinat/tableau_tuple.py

@@ -4926,7 +4926,6 @@ def max_row_in_component(tab, r):
             yield tableau_from_list(tab)
 
         # all done!
-        return
 
     def last(self):
         r"""

src/sage/combinat/words/suffix_trees.py

@@ -501,7 +501,6 @@ def show(self, *args, **kwds):
             sage: t.show()                                                              # needs sage.plot
         """
         self.plot(*args, **kwds).show()
-        return
 
 ################################################################################
 # Suffix Trees
@@ -656,7 +655,6 @@ def _process_letter(self, letter):
         # set the active state
         s, k = self._canonize(s, (k, i))
         self._active_state = (s, (k, i+1))
-        return
 
     def _test_and_split(self, s, k_p, letter):
         r"""
@@ -918,7 +916,6 @@ def show(self, word_labels=None, *args, **kwds):
             sage: t.show(word_labels=False)                                             # needs sage.plot
         """
         self.plot(word_labels=word_labels, *args, **kwds).show()
-        return
 
     #####
     # Various methods
@@ -1115,7 +1112,6 @@ def to_explicit_suffix_tree(self):
             end_state, r = self._test_and_split(s, (k, i-1), end_of_string)
         # remove the end of string symbol from the word
         self._letters.pop()
-        return
 
     def edge_iterator(self):
         r"""

src/sage/databases/cubic_hecke_db.py

@@ -1153,7 +1153,6 @@ def update_basis_extensions(self, new_basis_extensions):
         """
         self._data_library.update({self.section.basis_extensions: new_basis_extensions})
         self.write(self.section.basis_extensions)
-        return
 
 
 # -----------------------------------------------------------------------------