chore: Update Slack invitation link

Updated the expired Firecracker slack workspace link
in index.html with a new valid one.

Author: xmarcalx

index.html

@@ -146,7 +146,7 @@
             <span>Join our GitHub Community</span>
           </a>
           <a
-            href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1fecwrorm-x5URTlOzBR2fExTU2mWfug"
+            href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1zlb87h4z-NED1rBhVqOQ1ygBgT76wlg"
             class="css-button sta-hoverOFF"
           >
             <i class="icon-slack" aria-hidden="true"></i>
@@ -358,7 +358,7 @@
               </a>
               . You can chat with others in the community on the
               <a
-                href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1fecwrorm-x5URTlOzBR2fExTU2mWfug"
+                href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1zlb87h4z-NED1rBhVqOQ1ygBgT76wlg"
               >
                 Firecracker Slack workspace
               </a>
@@ -421,7 +421,7 @@
             <span>Join our GitHub Community</span>
           </a>
           <a
-            href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1fecwrorm-x5URTlOzBR2fExTU2mWfug"
+            href="https://join.slack.com/t/firecracker-microvm/shared_invite/zt-1zlb87h4z-NED1rBhVqOQ1ygBgT76wlg"
             class="css-button3 sta-hoverOFF"
           >
             <i class="icon-slack" aria-hidden="true"></i>