fix: test: Allow re-run of mkeys system test

On some slow systems, the test might intermittently fail due to inherent
timing issues. In our CI, this most often happens in the
system:gcc:8fips:amd64 jobs.

Closes #3098

Merge branch '3098-allow-re-run-of-mkeys-test' into 'main'

See merge request isc-projects/bind9!9732

bin/tests/system/mkeys/tests_sh_mkeys.py

@@ -11,6 +11,8 @@
 
 import pytest
 
+import isctest.mark
+
 pytestmark = [
     pytest.mark.algorithm_set("ecc_default"),
     pytest.mark.extra_artifacts(
@@ -49,5 +51,6 @@ pytestmark = [
 ]
 
 
+@isctest.mark.flaky(max_runs=2)  # GL#3098
 def test_mkeys(run_tests_sh):
     run_tests_sh()