Skip failing msan tests

These tests started failing after https://crrev.com/c/1046657.

R=ahaas@chromium.org

Bug: v8:7748
No-Try: true
Change-Id: I67b44b144e5e62c5a88cbf6683e0678e6eab1dc6
Reviewed-on: https://chromium-review.googlesource.com/1051243Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53094}

test/cctest/cctest.status

@@ -198,6 +198,11 @@
 ['msan == True', {
   # ICU upstream issues.
   'test-strings/CountBreakIterator': [SKIP],
+
+  # https://crbug.com/v8/7746
+  # MSan issues after landing https://crrev.com/c/1046657
+  'test-serialize/StartupSerializerOnce': [SKIP],
+  'test-serialize/StartupSerializerTwice': [SKIP],
 }],  # 'msan == True'
 
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