[extract-inputs] Search for PRs by SHA using "list pull requests" of 100 recently updated

Add as fallback between "get PRs for commit SHA" and "search".

We should extract the existing code from `context.js` and create a helper method `listPullRequestsForCommit(head_owner, head_repo, head_sha, base_owner, base_repo)`, which tries the following:

1. repos.listPullRequestsAssociatedWithCommit(head_owner, head_repo, head_sha)
- Should work on fork and non-fork PRs to public, and non-fork PRs to private
2. pulls.list(base_owner, base_repo, orderby: updated-desc), client-side filter by head_sha
- Should work on fork PRs to private
- Max 100 pulls per API call, so maybe only search first page?
3. search(base_owner, base_repo, head_sha)
- Should work on fork and non-fork PRs to public and private
- Low rate limit of 30 req/min