Fix an HTML entity and en-dash spacing.

The correct escaped version would be – but the file and pipeline
are already handling non-ASCII characters like the copyright symbol
fine, so there's no reason this needs to be escaped.

Author: amartini51

TSPL.docc/footer.html

@@ -12,7 +12,7 @@
 <footer id="footer" role="contentinfo" hidden>
   <div class="container">
     <div>
-      <p class="copyright">Copyright © 2014 &en; 2023 Apple Inc. and the Swift project authors. All rights reserved.</p>
+      <p class="copyright">Copyright © 2014–2023 Apple Inc. and the Swift project authors. All rights reserved.</p>
       <p>This document is made available under a <a rel="license" href="https://creativecommons.org/licenses/by/4.0/" style="color: #09f">Creative Commons Attribution 4.0 International (CC BY 4.0) License</a>.</p>
       <p class="trademark">Swift and the Swift logo are trademarks of Apple Inc.</p>
       <p class="privacy">