review.sh: make it easier to overwrite a copy

[annevk]

Review Draft publication goes relatively well (though see #348) as per https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#review-drafts. One problem is recovering from build failures.

When hitting a build failure my current process is something like this:

1. Create a separate PR to address the build failure.
2. Rebase the RD PR.
3. Change the review.sh script by commenting out four lines (starting with git checkout main) to avoid it creating a new branch.
4. Make review.sh executable via chmod 755 review.sh (755 is prolly too much?).
5. Run it.
6. Rebase the RD PR again folding the new commit into the previous one.
7. Force push.
8. Hopefully all is well now.

Step 1 is always needed. Ideally step 2 through 7 would be replaced by a single step, e.g., ./review.sh redo.

Anyone else have thoughts on this?