ci: install GitHub CLI for distro validation

[Bjordis Collaku (bjordiscollaku)]

Summary

• Install GitHub CLI through APT in every trusted distro validation job before its scripts call the GitHub API.
• Restore kernel context resolution, Check Run creation and completion, distro dispatch, failure reporting, and callback validation.
• Remove reliance on the ephemeral runner image providing gh.

Root Cause

Smoke test PR #82 completed its kernel build and uploaded Debian packages successfully. The trusted workflow_run then failed in resolve-distro-validation-context.sh because gh was not installed, so no Check Run was created and no distro validation request was dispatched.

• Smoke PR: [SMOKE TEST] Validate Canonical premerge distro pipeline #82
• Failed trusted run: https://github.com/qualcomm-linux/pkg-linux-qcom-canonical/actions/runs/32427808156

Validation

• Parsed the workflow as YAML.
• Validated the workflow with Actionlint and ShellCheck.
• Confirmed all five jobs that invoke GitHub API helpers install gh first.
• Confirmed Ubuntu provides the required ARM64 gh package.
• Confirmed the workflow diff is clean and limited to the trusted validation workflow.

Counterpart distro fix: https://github.com/qualcomm-linux/qcom-distro-images/pull/127

The complete live request, distro build, callback, and Check Run chain will be rerun after both fixes are available on main.