automation: Update gitlabrunner-image to version 15

This MR contains the following updates:

Package	Update	Change
gitlabrunner-image	major	v14.10.1 -> v15.0.0

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this MR and you won't be reminded about this update again.

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• If you want to rebase/retry this MR, click this checkbox.

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This MR has been generated by Renovate Bot. The local configuration can be found in the local Renovate Bot repository.