Mark flaky test as --no-opt

TBR=sigurds@chromium.org

Change-Id: Ibc6bcb9f9576a34d909a8f0d0fbdc2899f0b671e
Reviewed-on: https://chromium-review.googlesource.com/1127369Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54276}

test/debugger/debug/debug-modules-set-variable-value.js

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // MODULE
-// Flags: --no-always-opt
+// Flags: --no-always-opt --no-opt
 
 // The first part of this file is copied over from debug-set-variable-value.js
 // (a few tests were removed because they make no sense for modules). The second