Add tests directory to watchlist

No-Try: true
Change-Id: I6e8f1130ed0fe89d4f5ca8e9ff01ff68f13cbbdf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4221699
Commit-Queue: Almothana Athamneh <almuthanna@chromium.org>
Auto-Submit: Almothana Athamneh <almuthanna@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#85679}

WATCHLISTS

@@ -104,6 +104,9 @@
     'trap-handler': {
       'filepath': 'src/trap-handler/',
     },
+    'tests': {
+      'filepath': 'test/',
+    },
   },
 
   'WATCHLISTS': {
@@ -177,5 +180,8 @@
       'mark@chromium.org',
       'mseaborn@chromium.org',
     ],
+    'tests': [
+      'almuthanna+watch@chromium.org',
+    ],
   },
 }