change polynomial ring notation to remove lint error

src/sage/combinat/symmetric_group_algebra.py

@@ -2103,7 +2103,8 @@ def all_roots_field():
             required_square_roots = flatten([[QQ(q).numerator(),QQ(q).denominator()] if q in QQ else q for q in required_square_roots])
             K = self.base_ring()
             for n in set(required_square_roots):
-                R.<x> = PolynomialRing(K)
+                R = PolynomialRing(K, 'x')
+                x = R.gen()
                 if (x**2 - n).is_irreducible():
                     gen_name = "sqrt"+str(n).replace("/","over")
                     K = K.extension(sqrt(n).minpoly(),names=gen_name)