t7519: disable external GIT_TEST_FSMONITOR variable

The GIT_TEST_FSMONITOR variable was created specifically so the
t7519-status-fsmonitor.sh test script could tweak the expected
behavior depending on its value. However, if we set it externally
to use the Watchman integration, then it breaks the initial tests
that demonstrate behavior _without_ the fsmonitor feature.

Disable this variable at the start of the script.

Signed-off-by: Derrick Stolee <[email protected]>

Author: derrickstolee

t/t7519-status-fsmonitor.sh

@@ -8,6 +8,9 @@ test_description='git status with file system watcher'
 # "git update-index --fsmonitor" can be used to get the extension written
 # before testing the results.
 
+# Disable an external value, as we will set it directly as needed.
+GIT_TEST_FSMONITOR=""
+
 clean_repo () {
 	git reset --hard HEAD &&
 	git clean -fd