Allow repo fork even when `shared_runners_enabled` conflicts with its group
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=364303) </details> <!--IssueSummary end--> ## Problem An Ultimate SaaS customer reports that when they attempt to fork the [GitLab docker-machine](https://gitlab.com/gitlab-org/ci-cd/docker-machine) repo to their project, it fails because they do not have shared runners enabled on the project. This is very similar to https://gitlab.com/gitlab-org/gitlab/-/issues/276930. I duplicated the behavior on a [namespace that has shared runners disabled](https://gitlab.com/gitlab-gold/mgibsongl). The network tab on the browser inspector reveals a `409` error when attempting to fork, and the error message is: ``` {"message":{"shared_runners_enabled":["cannot be enabled because parent group does not allow it"]}} ``` ## Proposed solution I believe the proposed solutions provided on the related issue I linked to above can probably apply here, as well. * Keep project value if `Allow projects and subgroups to override the group` setting is set, as it already does * Otherwise inherit group setting of disabled, if a project has enabled set * Keep project setting of enabled/disabled, if group setting is enabled. [Zendesk ticket](https://gitlab.zendesk.com/agent/tickets/296238) (internal)
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