[test] skip code-coverage-ad-hoc for gc fuzzer.

R=machenbach@chromium.org

Bug: v8:7350
Change-Id: I048ea31afaa6aeb1bee6b9ef91e1afa31324ebcd
Reviewed-on: https://chromium-review.googlesource.com/880624Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50792}

test/mjsunit/mjsunit.status

@@ -641,6 +641,10 @@
   'ignition/regress-672027': [PASS, ['tsan', SKIP]],
   'string-replace-gc': [PASS, SLOW, ['mode == debug', SKIP]],
 
+  # Unsuitable for GC fuzzing because coverage information is lost on GC.
+  'code-coverage-ad-hoc': [SKIP],
+  'code-coverage-precise': [SKIP],
+
   # Fails allocation on tsan.
   'es6/classes': [PASS, ['tsan', SKIP]],
 }],  # 'gc_fuzzer'