chore: use default nixos test to test pg_graphql extension

Author: jfroche

nix/ext/tests/default.nix

@@ -185,6 +185,7 @@ builtins.listToAttrs (
       "hypopg"
       "index_advisor"
       "pg_cron"
+      "pg_graphql"
       "pg_net"
       "vector"
       "wrappers"