[test] Skip flaky test

Bug: v8:6132
NOTRY=true
TBR=jgruber@chromium.org,eholk@chromium.org

Change-Id: Idd706e5bb08f1890f6edc69792238114aadf220b
Reviewed-on: https://chromium-review.googlesource.com/459517Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44098}

test/mjsunit/mjsunit.status

@@ -693,6 +693,7 @@
 
   # BUG(v8:6132).
   'wasm/grow-memory': [PASS, ['gc_stress', SKIP]],
+  'wasm/import-memory': [PASS, ['gc_stress', SKIP]],
 }],  # variant == wasm_traps
 
 ]