tests: conditionalize out tests that msys is mangling This was exposed by ac0a87160012. The paths for convert and ssh respectively are being turned into: $TESTTMP\bzr+ssh:\foobar@selenic.com\baz\.hg 'C:\\C:\\Users\\Matt\\AppData\\Local\\Temp\\hgtests.8awa9x\\child1\\test-ssh-bundle1.t-sshv2\\nonexistent\\.hg The errno value raised is 123, and the message is The filename, directory name, or volume label syntax is incorrect