drop caching; we as we do not add composer.lock to git anyway

.github/workflows/php.yml

@@ -19,17 +19,6 @@ jobs:
     - name: touch config.local.php
       run: touch config.local.php && php -v
 
-    - name: Get Composer Cache Directory
-      id: composer-cache
-      run: |
-        echo "::set-output name=dir::$(composer config cache-files-dir)"
-    - uses: actions/cache@v1
-      with:
-        path: ${{ steps.composer-cache.outputs.dir }}
-        key: ${{ runner.os }}-composer-${{ hashFiles('composer.lock') }}
-        restore-keys: |
-          ${{ runner.os }}-composer-
-
     - name: Install dependencies
       run: composer install --prefer-dist --no-progress --no-suggest