Improve release script

[romaricpascal]

What

1. The release script runs an unnecessary gh pr merge after having waited for the PR to be merged on GitHub. This is a remnant from when the script was only waiting for the PR to be approved and doesn't block the script, but could use a little tidy up.
2. A failed npm publish still ends with a 'Publish successful' displayed in the console, even though the publishing didn't get through as expected
3. During our release of 13.16.1, the script tried to publish 13.16.0 to npm rather than the new version.¹

Why

During the release of 13.16.1, we noticed a couple of issues with the release script.

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Smaller issues have been created to address these 3 problems
• The work in each issue has been completed

Footnotes

1. Might be worth checking which working directory the npm run clean-publish command runs into. 13.16.0 was the version number in the Git working directory from which the ./scripts/prepare-release was run. ↩