Add attributes to git* modules (#5947)

Add attributes to git* modules.

plugins/modules/gitlab_group_variable.py

@@ -26,6 +26,13 @@ requirements:
 extends_documentation_fragment:
   - community.general.auth_basic
   - community.general.gitlab
+  - community.general.attributes
+
+attributes:
+  check_mode:
+    support: full
+  diff_mode:
+    support: none
 
 options:
   state:
@@ -99,8 +106,6 @@ options:
           - The scope for the variable.
         type: str
         default: '*'
-notes:
-- Supports I(check_mode).
 '''