tests: skip test-git-interop.t on Windows

Casefolding isn't handled in dirstate yet, triggering a bunch of assertions.
But while this is more correctly `no-icasefs`, it's more likely to get attention
if someone sees it.  I'd just rather not have it adding to the noise on Windows
for now.

Differential Revision: https://phab.mercurial-scm.org/D10312

tests/test-git-interop.t

@@ -1,4 +1,4 b''
-#require pygit2
+#require pygit2 no-windows
 
 Setup:
   $ GIT_AUTHOR_NAME='test'; export GIT_AUTHOR_NAME