Bug 1834742: Enable CET compatible modules only for the GPU process in Nightly. r=handyman

Differential Revision: https://phabricator.services.mozilla.com/D178927

modules/libpref/init/StaticPrefList.yaml

@@ -13710,7 +13710,7 @@
 
 -   name: security.sandbox.gpu.shadow-stack.enabled
     type: RelaxedAtomicBool
-    value: false
+    value: @IS_NIGHTLY_BUILD@
     mirror: always
 
 -   name: security.sandbox.gmp.shadow-stack.enabled