t5580-unc-paths.sh test failures

[me-and]

Using the Cygwin time machine, whatever has broken was broken by the change from cygport v0.36.1-1 and v0.36.2-1.

[me-and]

cygwin/cygport@8b33f70 looks most suspicious from a quick skim.

Full changelog is at cygwin/cygport@0.36.1...0.36.2

[me-and]

And bisecting cygport confirms it: the test fails when using cygwin/cygport@8b33f70 and succeeds when using cygwin/cygport@9b231ea.

[me-and]

Okay, so the issue is because Cygport is enabling case sensitivity on the build directory, and that's causing the tests to fail. I think that won't actually cause a change in Git's behaviour, though, so this isn't blocking the release.

It's not clear what the correct solution here is, but I can at least block out the tests and release.