fix(modules/gitlab_runner): Fix exception in check mode on new runners (#10918)
* fix(modules/gitlab_runner): Fix exception in check mode on new runners
When a new runner is added in check mode, the role used to throw an
exception. Fix this by returning a valid runner object instead of a
boolean.
Fixes#8854
* docs: Add changelog fragment
(cherry picked from commit 7e666a9c31)
Co-authored-by: carlfriedrich <carlfriedrich@posteo.de>
e757adbfca