PHP 8 support (#542)

* PHP 8 support, test workflow syntax

* Try using a custom data structure in the workflow

* Try using matrix include

* Default PHP target

* single include

* fix composer package name

* [WIP] Try using dev-master for valuestore

* Update spatie/valuestore constraint to be stable

docker-compose.yml

@@ -3,6 +3,9 @@ services:
     test:
         build:
             context: .
+            args:
+              PHP_VERSION: ${PHP_VERSION}
+              PHP_TARGET: ${PHP_TARGET}
         depends_on:
             mysql:
                 condition: service_healthy