fix(actions): don't show branch-filtered push workflows as skipped in pull requests

[bircni]

Closes #38351

Problem

A push-only workflow shows up as Skipped inside pull requests, where it should not appear at all.

Given two workflows:

# .gitea/workflows/push.yml
on:
  push:
    branches: [main]

# .gitea/workflows/pull.yml
on:
  pull_request:

Opening a PR from a feature branch surfaces the push workflow as a skipped check in the PR.

Cause

#38237 fixed required status checks getting stuck Pending when a workflow is excluded by a paths filter, by posting a CommitStatusSkipped status for filtered-out workflows. But matchPushEvent / matchPullRequestEvent returned detectFilteredOut for any filter mismatch — including a branch/tag mismatch.

So pushing to a feature branch, where the push workflow's branches: [main] filter excludes the ref, posted a skipped push status on that commit. Because the commit is the PR's head, the status leaked into the PR's checks.

[Zettat123]

Now the behavior is:

• path mismatch: create skipped commit status
• ref mismatch: do not create commit status

Do we want to keep this behavior inconsistent? AFAIK, GitHub doesn't create a commit status for either type of mismatch.

[wxiaoguang]

rubberstamp approve since I haven't really looked into the details, while the code itself looks good.

wait for more feedbacks for #38365 (comment)