Show errors that occur in GroupCallView using the error boundary

We were previously using the useGroupCallErrorBoundary hook to surface errors that happened during joining, but because that part is outside the GroupCallErrorBoundary it just ended up sending them to the app-level error boundary where they got displayed with a more generic message.

src/utils/test.ts

@@ -286,8 +286,9 @@ export class MockRTCSession extends TypedEventEmitter<
     super();
   }
 
-  public isJoined(): true {
-    return true;
+  public joined = true;
+  public isJoined(): boolean {
+    return this.joined;
   }
 
   public withMemberships(