Replace ubuntu-26.04 with ubuntu-slim

Author: vstinner

.github/workflows/new-bugs-announce-notifier.yml

@@ -10,7 +10,7 @@ permissions:
 
 jobs:
   notify-new-bugs-announce:
-    runs-on: ubuntu-26.04
+    runs-on: ubuntu-slim
     permissions:
       issues: read
     timeout-minutes: 10