Upgrade the cache Github action

Version 2 of the cache Github action has been deprecated, and upgrading
to a more recent version is required, so this commit upgrades from v2 to
v4.

Author: aag

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['8.1', '8.2', '8.3']
+        php-versions: ['8.1', '8.2', '8.3', '8.4']
     steps:
       - name: Checkout
         uses: actions/checkout@v2
@@ -45,7 +45,7 @@ jobs:
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
       - name: Cache dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}