pytest_plugin(fix[gitconfig]): Always write config, remove early return

why: The fixture was returning early if .gitconfig already existed,
even if the file was empty or missing protocol.file.allow=always.
This caused failures on Arch Linux build where git/container setup
creates an incomplete .gitconfig before the fixture runs.

what:
- Remove early return that skipped writing when file exists
- Fixture now always writes the full config with protocol.file.allow
- Follow-up to #510, #511 for #509

Author: tony

src/libvcs/pytest_plugin.py

@@ -154,9 +154,6 @@ def gitconfig(
     """Return git configuration, pytest fixture."""
     gitconfig = user_path / ".gitconfig"
 
-    if gitconfig.exists():
-        return gitconfig
-
     gitconfig.write_text(
         textwrap.dedent(
             f"""