Fix "Join the Tekton Slack!" link

Old link was broken:

This link is no longer active

To join this workspace, you’ll need to ask the person who originally invited you for a new link.

New one is from https://github.com/tektoncd/community/blob/main/contact.md#slack

layouts/partials/community-links.html

@@ -34,7 +34,7 @@ <h2>Reach out</h2>
         <p>Join our community spaces:</p>
         <ul>
           <li><i class="fab fa-slack fa-fw"></i>
-            <a href="https://join.slack.com/t/tektoncd/shared_invite/enQtNjQ1NjQzNTQ3MDQwLTc5MWU4ODg3MGJiYjllZjlmMWI0YWFlMzJjMTkyZGEyMTFhYzY1ZTkzZGU0M2I3NGEyYjU2YzNhOTE4OWQyZTM">
+            <a href="https://join.slack.com/t/tektoncd/shared_invite/zt-23f3gmgch-3pKwLCrnh2~HLttlX_4djg">
               Join the Tekton Slack!</a>
           </li>
           <li><i class="fab fa-twitter fa-fw"></i>