Improved how venv driver finds Python executables.

The venv driver will now look on the system PATH for the Python
to use for creating new virtual environments.

src/venv_management/ext/drivers/venv/driver.py

@@ -53,7 +53,14 @@ def make_virtual_env(self, name, *, python=None, project_path=None, packages=Non
             self._venvs_dirpath.mkdir(parents=True, exist_ok=True)
 
         virtualenv_dirpath = self._venvs_dirpath / name
-        python_exe = Path(python or sys.executable)
+
+        if python:
+            python_exe = Path(python)
+            if not python_exe.is_file():
+                if (found := shutil.which(python)) is not None:
+                    python_exe = Path(found)
+        else:
+            python_exe = Path(sys.executable)
 
         if not python_exe.is_file():
             raise PythonNotFound(f"Could not locate Python {python}")