[PHP8] Add initial compatibility (#1106)

* gha: run on PHP8 too

The composer.json constraint is unbound, so it's already "allowed" at least.

* gha: remove php-cs-fixer when running unit tests

- not necessary anyway
- not compatible with PHP8 currently

* gha: lumen 6 and 7 don't support PHP8

* composer.json: allow spatie/phpunit-snapshot-assertions 4.* for PHP8 compatibility

* php8-compat: Method ReflectionParameter::getClass() is deprecated

* php8-compat: adapt expected error message depending on PHP version

* composer.json: bump mockery to 1.3.3 minimum

This is the minimum version also supporting PHP8

* gha: disable prefer-lowest for PHP8

Some lower version requirements like doctrone/dbal won't work and
would require at least dbal 2.12.0, which in turn doesn't support PHP 7.2
anymore.

So instead of bumping dbal and excluding PHP 7.2 users, we ignore the
lowest version for PHP 8 for the time being.

* Update CHANGELOG.md

.github/workflows/run-integration-tests.yml

@@ -18,9 +18,13 @@ jobs:
             COMPOSER_NO_INTERACTION: 1
         strategy:
             matrix:
-                php: [7.4, 7.3, 7.2]
+                php: [8.0, 7.4, 7.3, 7.2]
                 lumen: [8.*, 7.*, 6.*]
                 exclude:
+                  - lumen: 6.*
+                    php: 8.0
+                  - lumen: 7.*
+                    php: 8.0
                   - lumen: 8.*
                     php: 7.2
         name: P${{ matrix.php }} - Lumen${{ matrix.lumen }}

.github/workflows/run-tests.yml

@@ -19,12 +19,14 @@ jobs:
 
     strategy:
       matrix:
-        php: [7.4, 7.3, 7.2]
+        php: [8.0, 7.4, 7.3, 7.2]
         laravel: [8.*, 7.*, 6.*]
         dependency-version: [prefer-lowest, prefer-stable]
         exclude:
           - laravel: 8.*
             php: 7.2
+          - php: 8.0
+            dependency-version: prefer-lowest
 
     name: P${{ matrix.php }} - L${{ matrix.laravel }} - ${{ matrix.dependency-version }}
 
@@ -42,6 +44,7 @@ jobs:
     - name: Install dependencies
       run: |
         composer remove vimeo/psalm --no-update --dev
+        composer remove friendsofphp/php-cs-fixer --no-update --dev
         composer require "laravel/framework:${{ matrix.laravel }}" --no-update --no-progress
         composer update --${{ matrix.dependency-version }} --prefer-dist --no-progress