chore: pin GitHub Actions to commit SHAs

Author: nunomaduro

.github/workflows/ci.yml

@@ -16,18 +16,18 @@ jobs:
     steps:
 
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
 
     - name: Cache dependencies
-      uses: actions/cache@v2
+      uses: actions/cache@8492260343ad570701412c2f464a5877dc76bace # v2
       with:
         path: ~/.composer/cache/files
         key: dependencies-php-${{ matrix.php }}-composer-${{ hashFiles('composer.json') }}
         restore-keys: |
           dependencies-php-${{ matrix.php }}-composer-
 
     - name: Setup PHP
-      uses: shivammathur/setup-php@v2
+      uses: shivammathur/setup-php@accd6127cb78bee3e8082180cb391013d204ef9f # v2
       with:
         php-version: ${{ matrix.php }}
         extensions: mbstring, zip