test php8 compatibility

Author: Insolita

./workflows/test.yml

@@ -44,14 +44,14 @@ jobs:
 uses: actions/cache@v2
 with:
 path: ${{ steps.composercache.outputs.dir }}
-key: ${{ runner.os }}-php-${{ matrix.php-versions }}-${{ hashFiles('**/composer.json') }}
+key: ${{ runner.os }}-php-${{ matrix.php-versions }}-${{ matrix.phpunit-versions }}-${{ hashFiles('**/composer.json') }}
 restore-keys: |
-${{ runner.os }}-php-${{ matrix.php-versions }}
+${{ runner.os }}-php-${{ matrix.php-versions }}-${{ matrix.phpunit-versions }}
 
  - name: Install deps
 run: composer install --prefer-dist --no-progress --no-suggest --optimize-autoloader
 
-- name: Unit tests 8.x
+- name: Unit tests 8.x with phpunit:${{ matrix.phpunit-versions }}
 run: phpunit
 if: matrix.php-versions == '8.0' || matrix.php-versions == '8.1'