test: mark test-vm-timeout-* known issue tests flaky

These are known issues that can be flaky on certain platforms
because they rely entirely on timing differences.

PR-URL: #23743
Refs: #3020
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>

Author: jasnell

test/known_issues/known_issues.status

@@ -9,6 +9,8 @@ prefix known_issues
 [$system==win32]
 
 [$system==linux]
+test-vm-timeout-escape-nexttick: PASS,FLAKY
+test-vm-timeout-escape-promise: PASS,FLAKY
 
 [$system==macos]