Update runners to ubuntu-24.04 from deprecated ubuntu-20.04 label (#26483)

Co-authored-by: Bill Napier <[email protected]>

Author: google-admin

.github/workflows/generate.yaml

@@ -15,7 +15,7 @@ on:
 name: generate
 jobs:
   generate_one:
-    runs-on: ubuntu-20.04
+    runs-on: 'ubuntu-24.04'
     strategy:
       fail-fast: false
       max-parallel: 4