Increase test reruns for fetchlimit

The fetchlimit test has failed 8 times in the nightly CI over the past
three weeks. That makes the overall failure rate somewhere around 1 %,
which isn't a lot, but is still annoying when lots of testing is going
on.

bin/tests/system/fetchlimit/tests_sh_fetchlimit.py

@@ -25,6 +25,6 @@ pytestmark = pytest.mark.extra_artifacts(
 import isctest.mark
 
 
-@isctest.mark.flaky(max_runs=2)
+@isctest.mark.flaky(max_runs=3)
 def test_fetchlimit(run_tests_sh):
     run_tests_sh()