CI: bump actions/cache to v5 (Node 24)

actions/cache@v1-v4 declare Node 20, which GitHub now deprecates and
force-runs on Node 24. v5 is Node 24 native and removes the warning.

Author: dereuromark

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Cache dependencies
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ${{ steps.composercache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
@@ -105,7 +105,7 @@ jobs:
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Cache dependencies
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ${{ steps.composercache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}