Fix wording of comment in buildClientSchema (#3821)

Author: Cito

src/utilities/buildClientSchema.ts

@@ -65,8 +65,8 @@ export function buildClientSchema(
   introspection: IntrospectionQuery,
   options?: GraphQLSchemaValidationOptions,
 ): GraphQLSchema {
-  // Even even though `introspection` argument is typed in most cases it's received
-  // as untyped value from server, so we will do an additional check here.
+  // Even though the `introspection` argument is typed, in most cases it's received
+  // as an untyped value from the server, so we will do an additional check here.
   devAssert(
     isObjectLike(introspection) && isObjectLike(introspection.__schema),
     `Invalid or incomplete introspection result. Ensure that you are passing "data" property of introspection response and no "errors" was returned alongside: ${inspect(