feat: use default nixos extension test

And run pg_regress tests for pgtap as part of the unified extension tests

Author: jfroche

nix/ext/tests/default.nix

@@ -206,6 +206,7 @@ builtins.listToAttrs (
       "pg_graphql"
       "pg_jsonschema"
       "pg_net"
+      "pgtap"
       "vector"
       "wrappers"
     ]