Enable `assumeImmutableResults` in security_configuration provider

This commit solves https://gitlab.com/gitlab-org/gitlab/-/issues/331283
It enables `assumeImmutableResults` in the dast_site_validation provider.

ee/app/assets/javascripts/security_configuration/dast_site_validation/graphql/provider.js

@@ -5,5 +5,5 @@ import createDefaultClient from '~/lib/graphql';
 Vue.use(VueApollo);
 
 export default new VueApollo({
-  defaultClient: createDefaultClient(),
+  defaultClient: createDefaultClient({}, { assumeImmutableResults: true }),
 });