Skip crashing test on win64.

R=machenbach@chromium.org
BUG=v8:5920
NOTRY=true

Review-Url: https://codereview.chromium.org/2671713002
Cr-Commit-Position: refs/heads/master@{#42888}

test/cctest/cctest.status

@@ -215,6 +215,9 @@
 
   # BUG(5193): Flaky timeout.
   'test-sampler/LibSamplerCollectSample': [PASS, ['arch == x64', SKIP]],
+
+  # BUG(5920): Flaky crash.
+  'test-serialize/PartialSerializerContext': [PASS, ['arch == x64 and mode == debug', SKIP]],
 }],  # 'system == windows'
 
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