CI: align branch-introduced actions with master's Node.js 24 bump

Rebasing onto master (which migrated JS actions to Node.js 24 runtimes)
left a few action refs that this branch added in new steps still on the
old major versions. Bring them in line with master:

- ccache-setup read-only restore:   actions/cache/restore@v4 -> @v5
- smoke-test / os-check ccache save: actions/cache/save@v4    -> @v5
- ci-deps-image checkout:            actions/checkout@v4       -> @v5

.github/actions/ccache-setup/action.yml

@@ -69,7 +69,7 @@ runs:
     # read-only=true: restore the shared cache but never upload (PR runs).
     - name: Restore ccache (read-only)
       if: inputs.read-only == 'true'
-      uses: actions/cache/restore@v4
+      uses: actions/cache/restore@v5
       with:
         path: ~/.ccache
         # Same key shape as the save branch, for symmetry. This branch never

.github/workflows/ci-deps-image.yml

@@ -62,7 +62,7 @@ jobs:
     runs-on: ${{ matrix.runner }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - name: Resolve and download the .deb closure
         shell: bash

.github/workflows/os-check.yml

@@ -407,7 +407,7 @@ jobs:
       # restore above; PR/push runs never save, so PRs add nothing.
       - name: Save ccache (seed only)
         if: github.event_name == 'schedule'
-        uses: actions/cache/save@v4
+        uses: actions/cache/save@v5
         with:
           path: ~/.cache/ccache
           key: os-check-linux-ccache-${{ matrix.shard }}-${{ github.ref_name }}-${{ github.sha }}

.github/workflows/smoke-test.yml

@@ -167,7 +167,7 @@ jobs:
       # ccache that PR runs restore; PRs never save.
       - name: Save ccache
         if: github.event_name != 'pull_request' && steps.merge_check.outputs.skip != 'true'
-        uses: actions/cache/save@v4
+        uses: actions/cache/save@v5
         with:
           path: ~/.cache/ccache
           key: smoke-ccache-${{ github.ref_name }}-${{ github.sha }}