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.

(cherry picked from commit a299650a6f)

bin/tests/system/mkeys/tests_sh_mkeys.py

@@ -11,6 +11,8 @@
 
 import pytest
 
+import isctest.mark
+
 pytestmark = pytest.mark.extra_artifacts(
     [
         "delv.*",
@@ -45,5 +47,6 @@ pytestmark = pytest.mark.extra_artifacts(
 )
 
 
+@isctest.mark.flaky(max_runs=2)  # GL#3098
 def test_mkeys(run_tests_sh):
     run_tests_sh()