title: Swift, iOS15, UIKit, CollectionView header issue
body: <p>I am testing <strong>iOS15</strong> and some new functionalities of <strong>UIKit</strong>. I've encountered some issues, not sure how to solve them. <em><strong>I did not change that code</strong>. This is just a piece of code that worked perfectly with the iOS 14, now after updating my target, it throws an error.</em></p>
  <p>Xcode crashes the moment when my <strong>custom header</strong> for the <strong>UICollectionView</strong> of type <strong>UICollectionElementKindSectionHeader</strong> is being returned for the <strong>dataSource</strong>. Here is my code:</p>
  <pre><code>private func configureDataSource() {
        dataSource = UICollectionViewDiffableDataSource&lt;Section, Follower&gt;(collectionView: collectionView, cellProvider: { (collectionView, indexPath, followers) -&gt; UICollectionViewCell? in
           let cell = collectionView.dequeueReusableCell(withReuseIdentifier: FollowerCell.reuseId, for: indexPath) as! FollowerCell
           cell.set(on: followers)
           return cell
        })
        
        dataSource.supplementaryViewProvider = { (collectionView, kind, indexPath) in
           let header = collectionView.dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader,
                                                                        withReuseIdentifier: FollowersCollectionHeaderView.reuseId,
                                                                        for: indexPath) as! FollowersCollectionHeaderView
           
           header.set(with: self.user)
           return header
        }
     }
  </code></pre>
  <p>The log says:</p>
  <blockquote>
  <p>the view returned from
  -collectionView:viewForSupplementaryElementOfKind:atIndexPath: does not match the element kind it is being used for. When asked for a view
  of element kind 'FollowersCollectionHeaderView' the data source
  dequeued a view registered for the element kind
  'UICollectionElementKindSectionHeader'.</p>
  </blockquote>
  <p>I did cast <strong>UICollectionElementKindSectionHeader</strong> to <strong>FollowersCollectionHeaderView</strong>, therefore I am not sure what is the issue here.</p>
  <p>I've watched <strong>WWDC21</strong> <strong>what's new in UIKit</strong> but haven't seen any mentioning of any change for that particular code.</p>
  <p>Any suggestions, what to fix in that code?</p>