GH Actions: simplify Composer caching

... by using the `ramsey/composer-install` action.

Ref: https://github.com/marketplace/actions/install-composer-dependencies

Author: jrfnl

.github/workflows/push.yml

@@ -102,19 +102,10 @@ jobs:
           GITHUB_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: phive --no-progress install --copy --trust-gpg-keys ${{ env.phiveGPGKeys }} phpunit:^8.5
 
-      - name: Get composer cache directory
-        id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
-
-      - name: Cache dependencies
-        uses: actions/cache@v2.1.4
+      - name: Install Composer dependencies & cache dependencies
+        uses: "ramsey/composer-install@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 --no-interaction --prefer-dist --optimize-autoloader
+          composer-options: --optimize-autoloader
 
       - name: Run PHPUnit
         continue-on-error: true
@@ -198,19 +189,10 @@ jobs:
           tools: psalm
           ini-values: memory_limit=2G, display_errors=On, error_reporting=-1
 
-      - name: Get composer cache directory
-        id: composer-cache
-        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
-
-      - name: Cache dependencies
-        uses: actions/cache@v2.1.4
+      - name: Install Composer dependencies & cache dependencies
+        uses: "ramsey/composer-install@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 --no-interaction --prefer-dist --optimize-autoloader
+          composer-options: --optimize-autoloader
 
       - name: Run psalm
         run: psalm --output-format=github