Disallow the rebase without pipeline on certain settings

What does this MR do and why?

This prevents the rebease without a pipeline button to show if the pipelines must succeed merge option is enabled. Preventing the merge request widget from entering an state where the merge button is not shown.

#371253 (closed)

Screenshots or screen recordings

Pipelines must succeed disabled, skipped pipelines are considered successful disabled

Pipelines must succeed enabled, skipped pipelines are considered successful disabled

Pipelines must succeed enabled, skipped pipelines are considered successful enabled

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. With a project with either Merge commit with semi-linear history or Fast-forward merge merge methods enabled.
2. Go to a open MR that needs to rebased due to being out of date
3. Enable and disable the Pipelines must succeed and skipped pipelines are considered successful merge checks similar to the combinations in the screenshot and check for the presence of the rebase without a pipeline button

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.