test-util-filemonitor: Adapt to the FreeBSD inotify rename semantics

test-util-filemonitor: Adapt to the FreeBSD inotify rename semantics

Unlike on Linux, on FreeBSD renaming a file when the destination
already exists results in an IN_DELETE event for that existing file:

    $ FILEMONITOR_DEBUG=1 build/tests/unit/test-util-filemonitor
    Rename /tmp/test-util-filemonitor-K13LI2/fish/one.txt -> /tmp/test-util-filemonitor-K13LI2/two.txt
    Event id=200000000 event=2 file=one.txt
    Queue event id 200000000 event 2 file one.txt
    Queue event id 100000000 event 2 file two.txt
    Queue event id 100000002 event 2 file two.txt
    Queue event id 100000000 event 0 file two.txt
    Queue event id 100000002 event 0 file two.txt
    Event id=100000000 event=0 file=two.txt
    Expected event 0 but got 2

This difference in behavior is not expected to break the real users, so
teach the test to accept it.

Suggested-by: "Daniel P. Berrange" <berrange@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20240206002344.12372-4-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>