fix(connection-state-recovery): pin mongodb due breaking change

Between 5 -> 6, the return value of `findOneAndDelete` changed. It now returns the document or null directly, see 'https://github.com/mongodb/node-mongodb-native/blob/HEAD/etc/notes/CHANGES_6.0.0.md#findoneandx-family-of-methods-will-now-return-only-the-found-document-or-null-by-default-includeresultmetadata-is-false-by-default'

By pinning the version we'll mitigate potential breaking changes in future.

lib/index.ts

@@ -821,11 +821,11 @@ export class MongoAdapter extends Adapter {
       return Promise.reject("error while fetching session");
     }
 
-    if (!results[0]?.value || !results[1]) {
+    if (!results[0] || !results[1]) {
       return Promise.reject("session or offset not found");
     }
 
-    const session = results[0].value.data;
+    const session = results[0].data;
 
     // could use a sparse index on [_id, nsp, data.opts.rooms, data.opts.except] (only index the documents whose type is EventType.BROADCAST)
     const cursor = this.mongoCollection.find({