Clean up git submodule tests and delay Git status runner

[DefaultRyan]

Summary of the pull request

I noticed that the Git Extension unit tests were not running in CI. Also, while running them, I noticed certain things not getting cleaned up properly - I saw error messages from the "git status" as the test repo was being deleted, and the deletion often failed because a LibGit2Sharp.Repository was hanging on to some files under .git.

References and relevant issues

Detailed description of the pull request / Additional comments

On the cleanup side of things in the Git extension:

• Trying to open the "checked-in" submodule test repositories was failing for some unknown reason in CI pipelines, even though it worked locally. I suspect some file access/permissions weirdness. To fix, moved to cloning a test repo and make state modifications to it live in the test. "WE'LL DO IT LIVE!"
• When a file system change is detected, don't start running "git status" immediately, wait for the directory to go idle for a few seconds before attempting a status refresh.
• Added a missing Dispose() call inside RepositoryWrapper.Dispose()
• When calling into GitLocalRepository from a test, there is no repository cache, so we need to dispose the RepositoryWrapper we created for this call.
• Added FileExplorerSourceControlIntegrationUnitTest and FileExplorerGitIntegration.UnitTest to CI flow

Validation steps performed

• Ran unit tests to verify they clean up cleanly now.
• Built full project and verified that the Git integration still performs as expected.

PR checklist

• Closes #xxx
• Tests added/passed
• Documentation updated

[ssparach]

nit: consider catching and logging exception here