[test] Skip slow tests on gc fuzzer

TBR=sergiyb@chromium.org
NOTRY=true

Bug: v8:6972
Change-Id: I011302ff740dc65ab6a50545ad6e51a2ee32c1bc
Reviewed-on: https://chromium-review.googlesource.com/876094Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50730}

test/benchmarks/benchmarks.status

@@ -39,7 +39,8 @@
 
 ['gc_fuzzer', {
   # Too slow for gc fuzzing.
-  'octane/splay': [PASS, SLOW, ['tsan', SKIP]],
+  'octane/earley-boyer' : [PASS, SLOW, ['mode == debug', SKIP]],
+  'octane/splay': [SKIP],
   'octane/typescript': [SKIP],
 }],  # 'gc_fuzzer'
 ]

test/mjsunit/mjsunit.status

@@ -639,6 +639,7 @@
   'regress/regress-748069': [SKIP],
   'regress/regress-778668': [SKIP],
   'ignition/regress-672027': [PASS, ['tsan', SKIP]],
+  'string-replace-gc': [PASS, SLOW, ['mode == debug', SKIP]],
 
   # Fails allocation on tsan.
   'es6/classes': [PASS, ['tsan', SKIP]],