Update badges in README

[rbergen]

Description

This makes some changes to the Action status badge(s) at the top of the README. As the changes don't impact the project code, I will merge this without review if CI passes.

Contributing requirements

• [x] I read the contribution guidelines in CONTRIBUTING.md.
• [x] I understand the BlinkenPerBit metric, and maximized it in this PR.
• [x] I selected main as the target branch.
• [x] All code herein is subjected to the license terms in COPYING.txt.