Mark the autosign system test as flaky

The autosign test uses sleep in many cases to wait for something to
happen. This inevitably leads to an instability that manifests in our
CI. Allow an automatic rerun of the test to improve its stability.

bin/tests/system/autosign/tests_sh_autosign.py

@@ -10,5 +10,9 @@
 # information regarding copyright ownership.
 
 
+import isctest.mark
+
+
+@isctest.mark.flaky(max_runs=2)
 def test_autosign(run_tests_sh):
     run_tests_sh()