test: flag known flake

`test-inspector-async-hook-setup-at-signal` is also flaky on VS2017

PR-URL: #16941
Reviewed-By: Colin Ihrig cjihrig@gmail.com
Reviewed-By: Gireesh Punathil gpunathi@in.ibm.com

Author: refack

test/sequential/sequential.status

@@ -10,6 +10,7 @@ prefix sequential
 test-inspector-async-call-stack       : PASS, FLAKY
 test-inspector-bindings               : PASS, FLAKY
 test-inspector-debug-end              : PASS, FLAKY
+test-inspector-async-hook-setup-at-signal:  PASS, FLAKY
 
 [$system==linux]