tests: Fix compile warning in tracker-file-notifier-test
tests: Fix compile warning in tracker-file-notifier-test

Fixes GB#667786.

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker