Declare compatibility with Flow 8

The compatibility is only declared, but not tested yet.

Author: robertlemke

composer.json

@@ -5,7 +5,7 @@
     "license": "MIT",
     "require": {
         "php": "^7.1 || ^8.0",
-        "neos/flow": "^5.0 || ^6.0 || ^7.0 || dev-master",
+        "neos/flow": "^5.0 || ^6.0 || ^7.0 || ^8.0 || dev-master",
         "neos/cache": "*"
     },
     "autoload": {