Support Drupal 9

Author: MPParsley

composer.json

@@ -9,7 +9,7 @@
     },
     "require": {
         "drupal/coder": "^8.3",
-        "drupal/core": "^8.9",
+        "drupal/core": "^8.9 || ^9",
         "drupal/drupal-extension": "^4.1",
         "ergebnis/composer-normalize": "^2.8",
         "mglaman/phpstan-drupal": "^0.12.5",