[SPARK-57140][INFRA] Disable merge button in .asf.yaml

[Yicong-Huang]

What changes were proposed in this pull request?

This PR disables all GitHub merge buttons in .asf.yaml by setting squash and rebase to false (in addition to the existing merge: false):

  enabled_merge_buttons:
    merge: false
    squash: false
    rebase: false

Why are the changes needed?

Apache Spark merges pull requests exclusively through the dev/merge_spark_pr.py script, not through GitHub's web UI merge button. The current .asf.yaml still exposes the Squash and Rebase merge buttons, which can mislead committers into merging a PR directly from the GitHub UI and bypassing the canonical merge tooling. Disabling all merge buttons leaves the merge script as the only supported path to land a PR.

Does this PR introduce any user-facing change?

No. This only affects committer-facing repository settings on GitHub.

How was this patch tested?

Not applicable; this is a configuration-only change to .asf.yaml. The YAML was validated to parse correctly and to set all three merge buttons to false.

Was this patch authored or co-authored using generative AI tooling?

No.

[Yicong-Huang]

cc @dongjoon-hyun @HyukjinKwon @cloud-fan

[dongjoon-hyun]

Sorry but -1 because this is a violation of ASF guideline, @Yicong-Huang .

The guideline clearly says one of them must be true.

• https://github.com/apache/infrastructure-asfyaml/blob/main/README.md#merge-buttons

At least one of squash, merge, or rebase must be true.

When you make a change on ASF infra related stuff, please double check the ASF guideline first. Although this works in a way, you should update the upstream first. In this case, ASF guideline first.

[dongjoon-hyun]

You know that we can revisit this PR after revising the upstream, @Yicong-Huang . The upstream ASF guideline is not always true because it's also maintained by human.

[Yicong-Huang]

Thanks for pointing these out, @dongjoon-hyun. This makes sense, I will close this PR for now.
Yes, I recently worked with INFRA team on rulesets configs and other configurations in another project. I will follow up on this with the upstream first.

[dongjoon-hyun]

Thank you!