unittest: Disable racy test

When run on a slow/busy machine, the notification might happen in 2 or
more batches. It works most of the time, but it's causing the build to
fail intermittently.
5 jobs for master in 18 minutes and 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #279165
amd64 debian
asan-ubsan

00:08:44

failed #279164
amd64 debian
coverage

00:06:12

passed #279161
amd64 debian
linux

00:09:41

passed #279162
win32
win32

00:11:21

passed #279163
win64
win64

00:09:27

 
Name Stage Failure
failed
coverage Test
[       OK ] SamplesTests/ResumeTests.Rescan/9 (3830 ms)
[ RUN ] SamplesTests/ResumeTests.Rescan/10
[ OK ] SamplesTests/ResumeTests.Rescan/10 (2619 ms)
[ RUN ] SamplesTests/ResumeTests.Rescan/11
[ OK ] SamplesTests/ResumeTests.Rescan/11 (1873 ms)
[ RUN ] SamplesTests/ResumeTests.Rescan/12
samples: src/parser/ParserWorker.cpp:48: void medialibrary::parser::Worker::start(): Assertion `m_threads.size() == 0' failed.
/usr/bin/bash: line 79: 5636 Aborted (core dumped) ./samples
ERROR: Job failed: exit code 1