gh-36398: two minor details in groups
    
fixing the category of dual abelian groups

fixing one of those pesting `#needs` annotation


### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
    
URL: #36398
Reported by: Frédéric Chapoton
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/groups/abelian_gps/dual_abelian_group.py

@@ -37,6 +37,8 @@
 
     sage: # needs sage.rings.real_mpfr
     sage: Fd = F.dual_group(names='ABCDE', base_ring=CC)
+    sage: Fd.category()
+    Category of commutative groups
     sage: A,B,C,D,E = Fd.gens()
     sage: A(a)    # abs tol 1e-8
     -1.00000000000000 + 0.00000000000000*I
@@ -64,7 +66,7 @@
 #  Distributed under the terms of the GNU General Public License (GPL)
 #                  http://www.gnu.org/licenses/
 ###########################################################################
-
+from sage.categories.groups import Groups
 from sage.structure.category_object import normalize_names
 from sage.structure.unique_representation import UniqueRepresentation
 from sage.groups.abelian_gps.dual_abelian_group_element import (
@@ -129,7 +131,7 @@ def __init__(self, G, names, base_ring):
         self._group = G
         names = normalize_names(G.ngens(), names)
         self._assign_names(names)
-        AbelianGroupBase.__init__(self)  # TODO: category=CommutativeGroups()
+        AbelianGroupBase.__init__(self, category=Groups().Commutative())
 
     def group(self):
         """

src/sage/groups/artin.py

@@ -142,6 +142,7 @@ def coxeter_group_element(self, W=None):
         From an element of the Coxeter group it is possible to recover
         the image by the standard section to the Artin group::
 
+            sage: # needs sage.rings.number_field
             sage: B(b1)
             s1*s2*s3*s2
             sage: A(c0)