fix(CI): MySQL unit tests, use LTS for code coverage and drop EOL

Co-authored-by: Ferdinand Thiessen <opensource@fthiessen.de>
Co-authored-by: Joas Schilling <213943+nickvergessen@users.noreply.github.com>
Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

.github/workflows/phpunit-mysql.yml

@@ -53,9 +53,9 @@ jobs:
     strategy:
       matrix:
         php-versions: ['8.0']
-        mysql-versions: ['8.0', '8.1']
+        mysql-versions: ['8.0', '8.3']
         include:
-          - mysql-versions: '8.1'
+          - mysql-versions: '8.0'
             php-versions: '8.3'
             coverage: true