ci: update actions/cache to v2

Author: williamdes

.github/workflows/tests.yml

@@ -24,7 +24,7 @@ jobs:
                   extensions: posix, mbstring
                   coverage: xdebug
             - name: Cache module
-              uses: actions/cache@v1.0.3
+              uses: actions/cache@v2
               with:
                   path: ~/.composer/cache/
                   key: composer-cache