Merge branch 'es/test-cron-safety'

The test script had an incomplete and ineffective attempt to avoid
clobbering the testing user's real crontab (and its equivalents),
which has been completed.

* es/test-cron-safety:
  test-lib: fix non-functioning GIT_TEST_MAINT_SCHEDULER fallback

t/test-lib.sh

@@ -1962,6 +1962,7 @@ test_lazy_prereq DEFAULT_REPO_FORMAT '
 # Tests that verify the scheduler integration must set this locally
 # to avoid errors.
 GIT_TEST_MAINT_SCHEDULER="none:exit 1"
+export GIT_TEST_MAINT_SCHEDULER
 
 # Does this platform support `git fsmonitor--daemon`
 #