[PR #10918/7e666a9c backport][stable-11] fix(modules/gitlab_runner): Fix exception in check mode on new runners

changelogs/fragments/10918-gitlab-runner-fix-check-mode.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - gitlab_runner - fix exception in check mode when a new runner is created (https://github.com/ansible-collections/community.general/issues/8854).

plugins/modules/gitlab_runner.py

@@ -345,7 +345,10 @@ def create_or_update_runner(self, description, options):
     '''
     def create_runner(self, arguments):
         if self._module.check_mode:
-            return True
+            class MockRunner:
+                def __init__(self):
+                    self._attrs = {}
+            return MockRunner()
 
         try:
             if arguments.get('token') is not None: