[test] Mark slow test

NOTRY=true
TBR=herhut@chromium.org

Bug: v8:8164
Change-Id: I6748a6fc58c9910855f018cccc1d93a40d8c32ad
Reviewed-on: https://chromium-review.googlesource.com/1219692Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55811}

test/mjsunit/mjsunit.status

@@ -171,6 +171,7 @@
   'string-replace-gc': [PASS, SLOW],
   'wasm/asm-wasm-f32': [PASS, SLOW],
   'wasm/asm-wasm-f64': [PASS, SLOW],
+  'wasm/compare-exchange-stress': [PASS, SLOW],
   'wasm/embenchen/*': [PASS, SLOW],
   'wasm/grow-memory': [PASS, SLOW],
   'wasm/unreachable-validation': [PASS, SLOW],
@@ -657,7 +658,6 @@
   'es6/typedarray-of': [PASS, SLOW],
   'regress/regress-crbug-854299': [PASS, SLOW],
   'regress/wasm/regress-810973': [PASS, SLOW],
-  'wasm/compare-exchange-stress': [PASS, SLOW],
 }],  # 'isolates'
 
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