PATCH /session_launchers/<launcher_id> can silently discard invalid patches

[leafty]

In some cases, when performing PATCH /session_launchers/<launcher_id> with an invalid payload, the operation is marked as successful without raising a 422 validation error.

See:

renku-data-services/components/renku_data_services/session/core.py

Line 82 in 880ac80

def validate_session_launcher_patch(

The case patch.environment is not None and environment is None should be rejected as a validation error.

This issue could be fixed as part of #541.