Update GitHub Action workflows to actions/cache@v5

Keep this up to date in all nonbranches, because the node.js runtime for older
versions might get deprecated in the future and fixing this for all branches at
once is easier.

see 2650248

Author: TimWolla

.github/workflows/root.yml

@@ -20,7 +20,7 @@ jobs:
           # the correct commit hashes.
           fetch-depth: 0
       - name: Grab the commit mapping
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: branch-commit-cache.json
           # The cache key needs to change every time for the