[JENKINS-68562] Fix Repo checkouts on the built-in node for Windows controllers

[dwnusbaum]

See JENKINS-68562, which was filed against Git, but the same issue should apply here.

On Windows, Paths.get throws InvalidPathException for URL-like values such as https://whatever. This breaks the fixes for SECURITY-2478 in 3c8e623 for Jenkins controllers running on Windows that perform checkouts on the built-in node.

CC @Pldi23 @rsandell

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
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• Please describe what you did
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• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[dwnusbaum]

The rest of this test class uses spaces, so I did too, even though RepoScm uses tabs. IDK if there is a particular preference.

[Pldi23]

approved, identical to git plugin fix