feat(ext): use the generic postgres extension test for postgis

Thanks to the improvement related to the generated pg_upgrade script, we can now reuse the generic postgres extension test for postgis.

Author: jfroche

nix/ext/tests/default.nix

@@ -234,6 +234,7 @@ builtins.listToAttrs (
       "pg_jsonschema"
       "pg_net"
       "pgaudit"
+      "postgis"
       "vector"
       "wrappers"
     ]