docs(data/polynomial/algebra_map): fix a typo in a doc-string (#13989)

The doc-string talks about `comm_ring`, while the lemma uses `comm_semiring`.  I aligned the two to the weaker one!

src/data/polynomial/algebra_map.lean

@@ -54,7 +54,7 @@ lemma of_finsupp_algebra_map (r : R) :
 to_finsupp_injective (to_finsupp_algebra_map _).symm
 
 /--
-When we have `[comm_ring R]`, the function `C` is the same as `algebra_map R R[X]`.
+When we have `[comm_semiring R]`, the function `C` is the same as `algebra_map R R[X]`.
 
 (But note that `C` is defined when `R` is not necessarily commutative, in which case
 `algebra_map` is not available.)