Update style and add changelog entry

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)
+* Fixed deadlock which occurs when accessing the current user from within a callback from the user listener ([#7183](https://github.com/realm/realm-core/issues/7183))
 * Update existing std exceptions thrown by the Sync Client to use Realm exceptions. ([#6255](https://github.com/realm/realm-core/issues/6255), since v10.2.0)
 * Automatic client reset recovery on flexible sync Realms would apply recovered changes in multiple write transactions, releasing the write lock in between. This had several observable negative effects:
   - Other threads reading from the Realm while a client reset was in progress could observe invalid mid-reset state.

src/realm/object-store/sync/sync_manager.cpp

@@ -339,7 +339,7 @@ bool SyncManager::perform_metadata_update(util::FunctionRef<void(SyncMetadataMan
 std::shared_ptr<SyncUser> SyncManager::get_user(const std::string& user_id, const std::string& refresh_token,
                                                 const std::string& access_token, const std::string& device_id)
 {
-    auto user = std::shared_ptr<SyncUser>(nullptr);
+    std::shared_ptr<SyncUser> user;
     {
         util::CheckedLockGuard lock(m_user_mutex);
         auto it = std::find_if(m_users.begin(), m_users.end(), [&](const auto& user) {