ci: cancel other CI runs when `require-issue-link` closes a PR (#35849)

When the `require_issue_link` workflow closes an external PR for failing
the issue-link/assignee check, other CI workflows (lint, tests,
integration tests) keep running uselessly. This cancels all of them
immediately after closing the PR.

## Changes
- After closing the PR in the `check-issue-link` job's final step,
enumerate all `in_progress` and `queued` workflow runs matching the PR's
`head_sha` via `actions.listWorkflowRunsForRepo` and cancel each one
(skipping self via `context.runId`)
- Add `actions: write` permission to the job to allow cancellation API
calls