Disable file-watcher with system inotify on some tests

When file watcher is active via GIT_TEST_WATCHER_PATH, `ls-files -v`
output may be different (e.g. "H" becomes "W"). Disable file watcher
in those cases.

We could make ls-files turn 'W' back to 'H' for these cases, but not
sure it's worth the effort. The intention of running with
GIT_TEST_WATCHER_PATH is to exercise file watcher in somewhat real
scenarios and the remaining tests are more than enough for that.