Change function to expect tuple instead of list

Author: CalebVL

src/sage/rings/polynomial/symmetric_reduction.pyx

@@ -254,7 +254,7 @@ cdef class SymmetricReductionStrategy:
         return richcmp((left._parent, left._lm, left._tail),
                        (right._parent, right._lm, right._tail), op)
 
-    def gens(self) -> list:
+    def gens(self) -> tuple:
         """
         Return the tuple of Infinite Polynomials modulo which ``self`` reduces.