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

@@ -217,12 +217,13 @@ builtins.listToAttrs (
       "hypopg"
       "index_advisor"
       "pg_cron"
-      "pg_hashids"
       "pg_graphql"
+      "pg_hashids"
       "pg_jsonschema"
       "pg_net"
-      "pgaudit"
       "pg_tle"
+      "pgaudit"
+      "pgtap"
       "vector"
       "wrappers"
     ]