Mk `tests/__init__.py`, not sure where it went?

I must have had a local touched file but never committed or something?
Seems that new `pytest` requires a top level `tests` pkg in order for
relative `.conftest` imports to work.

tests/devx/conftest.py

@@ -22,7 +22,7 @@ from tractor.devx._debug import (
     _repl_fail_msg as _repl_fail_msg,
     _ctlc_ignore_header as _ctlc_ignore_header,
 )
-from conftest import (
+from ..conftest import (
     _ci_env,
 )