Update year in DocC documentation footer (#694)

Author: franklinsch

Sources/docc/DocCDocumentation.docc/footer.html

@@ -1,7 +1,7 @@
 <!--
   This source file is part of the Swift.org open source project
 
-  Copyright (c) 2021-2022 Apple Inc. and the Swift project authors
+  Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
   Licensed under Apache License v2.0 with Runtime Library Exception
 
   See https://swift.org/LICENSE.txt for license information
@@ -11,7 +11,7 @@
 <footer id="footer" role="contentinfo" hidden>
   <div class="container">
     <div>
-      <p class="copyright">Copyright © 2022 Apple Inc. All rights reserved.</p>
+      <p class="copyright">Copyright © 2023 Apple Inc. All rights reserved.</p>
       <p class="trademark">Swift and the Swift logo are trademarks of Apple Inc.</p>
       <p class="privacy">
         <a href="//www.apple.com/privacy/privacy-policy/">Privacy Policy</a>