Support publishing GitHub Checks from standalone Pipeline jobs (non-Multibranch)

### What feature do you want to see added?

### Feature Request

Support publishing GitHub Checks from standalone Pipeline jobs that are not configured as Multibranch Pipelines.

### Current Behavior

The GitHub Checks plugin works well for Multibranch Pipelines and jobs that have GitHub SCM metadata available through the SCM Source integrations.

However, many Jenkins installations also have scheduled, nightly, release, or maintenance pipelines implemented as regular Pipeline jobs.

These jobs may:

- Checkout the same GitHub repository.
- Build a specific branch or commit.
- Run on a cron schedule.
- Publish test results, coverage, and other reports.

But they are currently unable (or very difficult) to publish GitHub Checks because the plugin cannot determine the GitHub context in the same way it does for Multibranch jobs.

### Use Case

We have:

- Multibranch jobs for PR validation and branch builds.
- Separate nightly jobs triggered on a schedule.
- Separate release/verification jobs.

The nightly and release jobs build commits from GitHub repositories and generate valuable results that we would like to surface as GitHub Checks on the corresponding commit.

Since Multibranch Pipelines can only use a single Jenkinsfile per branch workflow, these scheduled jobs are intentionally implemented as separate Pipeline jobs rather than additional Multibranch projects.

### Proposed Solution

Allow GitHub Checks publication from standalone Pipeline jobs using withChecks

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_