Bump GHA action versions

Author: andrewnicols

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
                     php-version: ${{ matrix.php }}
                     coverage: none
             -   name: Cache Composer dependencies
-                uses: actions/cache@v3
+                uses: actions/cache@v4
                 with:
                     path: ~/.composer/cache
                     key: php-${{ matrix.php }}-composer-locked-${{ hashFiles('composer.lock') }}
@@ -50,7 +50,7 @@ jobs:
                     tools: cs2pr
                     coverage: none
             -   name: Cache Composer dependencies
-                uses: actions/cache@v3
+                uses: actions/cache@v4
                 with:
                     path: ~/.composer/cache
                     key: php-composer-locked-${{ hashFiles('composer.lock') }}