[mjsunit] Make optimization test more reliable

Change-Id: If0fb6e4a20c334610453e9fe648151abca681442
Reviewed-on: https://chromium-review.googlesource.com/1150154Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54696}

test/mjsunit/compiler/array-multiple-receiver-maps.js

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax --opt --no-always-opt
+// Flags: --no-stress-background-compile
 
 let id = 0;