Describe the feature or problem you’d like to solve

Essentially I would like to use the tool to pull down the code at the head of a specific PR in CI & other automated scripts w/ containerized machines a la kubernetes pods, etc., using only the PR's number.

This is currently possible by doing

gh repo clone myorg/myrepo
cd myrepo
gh pr checkout 123

however that can take a long time if the repository has an extensive history or a lot of files.

For these situations I don't need to clone my whole repo and would like to simply clone with --single-branch and --depth 1 and a PR's branch name to make it faster.

Proposed solution

Given the existing infrastructure in the CLI for parsing PR info, this should be straightfoward, and as simple as translating a --pr flag into git-clone's already-supported --branch flag.