Fixed actions on PHP 8 (#65)

Author: GrahamCampbell

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          tools: composer:v2
+          tools: composer:snapshot
           coverage: none
 
       - name: Setup Problem Matchers
@@ -67,7 +67,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          tools: composer:v2
+          tools: composer:snapshot
           coverage: none
 
       - name: Setup Problem Matchers