tests: add zsh completion test for Path arguments

[konuktor1-jpg]

Adds a small regression test for zsh path completion in tests/test_completion/test_completion_path.py.

The file already had a Bash completion test, but no zsh-specific assertion. This test checks that Path completion returns the _files signal for zsh.

Tested locally with:

• uv run pytest tests/test_completion/test_completion_path.py -q

[konuktor1-jpg]

Hi! This PR is currently blocked because it has no required label, and the workflows are awaiting maintainer approval. I think bug would fit this change since it adds a regression test for existing zsh path completion behavior. Could someone please add the appropriate label and approve the workflows?