[mjsunit] Disable newly introduced flaking test

Bug: v8:9360
Notry: true
Change-Id: Ic598601d18149bcde5660ae268e81936a3954f3c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1658151
Auto-Submit: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62147}

test/mjsunit/mjsunit.status

@@ -241,6 +241,9 @@
 
   # BUG(v8:9260)
   'tools/profviz': [SKIP],
+
+  # BUG(v8:9360)
+  'harmony/weakrefs/unregister-inside-cleanup5': [SKIP],
 }],  # ALWAYS
 
 ['novfp3 == True', {