Cache composer dependencies

Author: DevDavido

.github/workflows/tests.yml

@@ -24,6 +24,17 @@ jobs:
                   php-version: ${{ matrix.php }}
                   coverage: xdebug
 
+            - 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
+              with:
+                  path: ${{ steps.composer-cache.outputs.dir }}
+                  key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+                  restore-keys: ${{ runner.os }}-composer-
+
             - name: Install dependencies
               run: composer update --${{ matrix.dependency-version }} --prefer-source --no-interaction