test: deflake watch mode tests

PR-URL: #44621
Backport-PR-URL: #44976
Fixes: #44655
Reviewed-By: Benjamin Gruenbaum <[email protected]>

Author: MoLow

test/fixtures/watch-mode/event_loop_blocked.js

@@ -0,0 +1,4 @@
+console.log('running');
+Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0);
+console.log('don\'t show me');
+