Tests can fail due to .config/pkgdev/pkgdev.conf modifications

I observed that if I run `pytest` within a fresh `git clone` of this repository, some the tests failed. I realized this is caused by the tests still using my `.config/pkgdev/pkgdev.conf` file while testing. The following sample `pkgdev.conf` file demonstrates the problem: ```ini [DEFAULT] commit.signoff = true ``` Which leads to TestPkgdevCommitParseArgs::test_commit_signing && TestPkgdevCommitParseArgs::test_git_commit_args_passthrough failing. Not urgent, because it's easily worked around by removing that argument from `pkgdev.conf`. But we've got outside environment leaking into tests and causing issues.