Fixed useSyncExternalStoreWithSelector to update memoizedSnapshot on change (facebook#25968)

## Summary

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A proposed fix for the bug described in
facebook#25967

## How did you test this change?

See the issue linked above, test scenario included in the code sandbox:
https://codesandbox.io/s/fervent-ives-0vm9es?file=/src/App.jsx

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Author: jellevoost

packages/use-sync-external-store/src/useSyncExternalStoreWithSelector.js

@@ -93,6 +93,9 @@ export function useSyncExternalStoreWithSelector<Snapshot, Selection>(
       // to React that the selections are conceptually equal, and we can bail
       // out of rendering.
       if (isEqual !== undefined && isEqual(prevSelection, nextSelection)) {
+        // The snapshot still has changed, so make sure to update to not keep
+        // old references alive
+        memoizedSnapshot = nextSnapshot;
         return prevSelection;
       }