fix(VCST-4390): doubled notifications (#2090)

## Description

## References
### Jira-link:
https://virtocommerce.atlassian.net/browse/VCST-4390
### Artifact URL:

https://vc3prerelease.blob.core.windows.net/packages/vc-theme-b2b-vue-2.36.0-pr-2090-6bd4-6bd4f165.zip

Author: ivan-kalachikov

client-app/modules/push-messages/api/graphql/queries/getPushMessages/index.ts

@@ -16,12 +16,14 @@ export function useGetPushMessages(payload: MaybeRefOrGetter<GetPushMessagesQuer
   result.subscribeToMore({
     document: OnPushMessageCreatedDocument,
     updateQuery: (previousQueryResult, { subscriptionData }) => {
-      if (!subscriptionData.data) {
+      const newPushMessage = subscriptionData.data.pushMessageCreated;
+      const items = previousQueryResult.pushMessages?.items ?? [];
+      const alreadyExists = items.some((item) => item.id === newPushMessage.id);
+
+      if (!subscriptionData.data || alreadyExists) {
         return previousQueryResult;
       }
 
-      const newPushMessage = subscriptionData.data.pushMessageCreated;
-      const items = previousQueryResult.pushMessages?.items ?? [];
       const unreadCount = previousQueryResult.unreadCount?.totalCount;
       const unreadCountWithHidden = previousQueryResult.unreadCountWithHidden?.totalCount;