Fix composable-controller allowlist error by assigning messenger to its own variable

See MetaMask/core#4033

Author: MajorLift

app/core/Engine.ts

@@ -1354,12 +1354,8 @@ class Engine {
       }
     }
 
-    this.datamodel = new ComposableController<
-      EngineState,
-      Controllers[keyof Controllers]
-    >({
-      controllers,
-      messenger: this.controllerMessenger.getRestricted({
+    const composableControllerMessenger =
+      this.controllerMessenger.getRestricted({
         name: 'ComposableController',
         allowedActions: [],
         // Add `stateChange` event here and in the `GlobalEvents` type
@@ -1385,7 +1381,13 @@ class Engine {
           'SnapController:stateChange',
           'SubjectMetadataController:stateChange',
         ],
-      }),
+      });
+    this.datamodel = new ComposableController<
+      EngineState,
+      Controllers[keyof Controllers]
+    >({
+      controllers,
+      messenger: composableControllerMessenger,
     });
     this.context = controllers.reduce<Partial<typeof this.context>>(
       (context, controller) => ({