ci: update slack action vm version

Author: jorwoods

.github/workflows/slack.yml

@@ -5,7 +5,7 @@ on: [push, pull_request, issues]
 jobs:
   slack-notifications:
     continue-on-error: true
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     name: Sends a message to Slack when a push, a pull request or an issue is made
     steps:
       - name: Send message to Slack API