Commit-queue should automatically handle PRs with merge commits from the target branch

Some contributors merge into their PR branch from main rather than rebasing. We might not recommend this, but it shouldn't be a major issue. Unfortunately it seems that the commit-queue label can't handle this, and fails with:

error: commit ... is a merge but no -m option was given.
fatal: cherry-pick failed

Here's a example I just ran into: https://github.com/nodejs/node/pull/59375#issuecomment-3178324429. More examples here.

AFAICT this then always requires manually landing the PR, but it feels like we should be able to handle these automatically without much trouble.

先定位调用 cherry-pick 的 commit queue 处理逻辑，然后使用一个包含从 main 合并的 pull request 重现所报告的失败。完成的标准是 commit queue 能够自动处理此类 pull request，而无需手动 landing；该 issue 未指定任何文件或要运行的测试。