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

@@ -224,6 +224,7 @@ builtins.listToAttrs (
       "pg_stat_monitor"
       "pg_tle"
       "pgaudit"
+      "pgtap"
       "vector"
       "wal2json"
       "wrappers"