Add more logging in prepareExistingDirectory so users know why clean: false is not being respected

[dhirschfeld]

I'm setting clean: false and actions/checkout is still deleting the contents of the repository?!?

Syncing repository: org/repo
::group::Getting Git version info
Getting Git version info
  Working directory is '/home/runner/work/repo/repo'
  ##[debug]Getting git version
  /usr/bin/git version
  git version 2.40.1
  ##[debug]0
  ##[debug]git version 2.40.1
  ##[debug]
  ##[debug]Set git useragent to: git/2.40.1 (github-actions-checkout)
  ::endgroup::
::add-mask::***
Temporarily overriding HOME='/home/runner/work/_temp/92c432d1-96fd-4c7a-8b60-65883f63951b' before making global git config changes
Adding repository directory to the temporary git global config as a safe directory
/usr/bin/git config --global --add safe.directory /home/runner/work/repo/repo
##[debug]0
##[debug]
Deleting the contents of '/home/runner/work/repo/repo'  <---- ????????????
::group::Initializing the repository
<snip>

Grepping the source it appears that there are multiple other hidden conditions that will mean actions/checkout silently ignores the explicitly specified user config:

checkout/src/git-directory-helper.ts

Lines 22 to 32 in f095bcc

	// Check whether using git or REST API
	if (!git) {
	remove = true
	}
	// Fetch URL does not match
	else if (
	!fsHelper.directoryExistsSync(path.join(repositoryPath, '.git')) ||
	repositoryUrl !== (await git.tryGetFetchUrl())
	) {
	remove = true
	} else {

Because there is no logging in any of these conditions I'm left none-the-wiser why actions/checkout is ignoring my config (there is logging in some other conditions which set remove = true so I'm apparently not hitting those conditions).