Fix tests with recent Git
Recent versions of Git have a new warning to suppress. While at it, I fixed the tests when running with --tmpdir, since that might result in it not being empty.
Meet users and developers of Mercurial at the London Sprint, May 27-29th https://mercurial-scm.org/news/2026/0001-london-sprint
Recent versions of Git have a new warning to suppress. While at it, I fixed the tests when running with --tmpdir, since that might result in it not being empty.