Update the run-on setting to ubuntu-22.04 in .github/workflows/backport.yml

[LeafShi1]

Fixes #13332

Root Cause

From the logs, the backport PR was not generated because the Ubuntu 20.04 LTS set in the current workflow was removed on 2025-04-15, and we need to set up a new runner

Proposed changes

• Update the run-on setting to ubuntu-22.04 in .github/workflows/backport.yml

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR updates the GitHub workflow by switching the runner image from ubuntu-20.04 to ubuntu-22.04 to address compatibility issues.

• Changed the runs-on value to use ubuntu-22.04.

[Tanya-Solyanik]

Thank you, Leaf! Could you please investigate the same in the designer repo, but don't spend too much time on it.

[LeafShi1]

Thank you, Leaf! Could you please investigate the same in the designer repo, but don't spend too much time on it.

Backport PRs on the designer repo have always been created manually, without a workflow template.
For the Ubuntu update, I found an old version at https://github.com/microsoft/winforms-designer/blob/c44b2e5f0e19bcbab1bc7b041ec72eaa7d899fdb/eng/common/core-templates/job/source-build.yml#L61, but it doesn't seem to be used anywhere.