ci: fix necessary permissions for cleanup_caches and comment

This undoes de5edca29c,
because I failed to read the documentation.

.github/workflows/cleanup_caches.yml

@@ -9,7 +9,8 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
-permissions: {} # uses own token below
+permissions:
+  actions: write
 
 jobs:
   cache:

.github/workflows/comment.yml

@@ -9,7 +9,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
-permissions: {} # uses own token below
+permissions:
+  actions: read
+  contents: write
 
 jobs:
   pr_comment: