Merge branch 'fix-gitlab-ci-schema-nullable-filter' into 'master'

Allow YAML `null` value for `only` and `except` filters

See merge request gitlab-org/gitlab!79335

app/assets/javascripts/editor/schema/ci.json

@@ -764,6 +764,9 @@
     },
     "filter": {
       "oneOf": [
+        {
+          "type": "null"
+        },
         {
           "$ref": "#/definitions/filter_refs"
         },