Save string path to python instead of Path object in YAML

src/xfel_calibrate/calibrate.py

@@ -1061,7 +1061,7 @@ def run():
         'author': author,
     }
     metadata['python-environment'] = {
-        'path': user_venv,
+        'path': python_exe,
         'python-version': get_python_version(python_exe),
     }
     metadata.save()