Disable failing debug tests in gc-stress.

TBR=machenbach@chromium.org
BUG=v8:3776
LOG=N

Review URL: https://codereview.chromium.org/944833002

Cr-Commit-Position: refs/heads/master@{#26769}

test/mjsunit/mjsunit.status

@@ -245,7 +245,11 @@
   # Issue 3723.
   'regress/regress-3717': [SKIP],
   # Issue 3776.
+  'debug-constructor': [SKIP],
   'debug-stepframe': [SKIP],
+  'debug-stepout-scope-part2': [SKIP],
+  'debug-stepout-scope-part5': [SKIP],
+  'debug-stepout-scope-part6': [SKIP],
 }],  # 'gc_stress == True'
 
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