GitHub Action Badges
If you want to show the GitHub Actions status badge for one of your workflow, be aware that the URL has to reflect the action.
An GitHub action configuration file located in:
.github/workflow/markdownlint.yml
Could be reflected in a badge with the URL:

Like for example this badge for one of my repositories:
- The URL points to GitHub:
https://github.com
- My account:
jonasbn
- The relevant (this) repository:
til
- The workflows directory:
workflows
and this is theworkflows
directory located in the directory.github
, you do however have to addactions
before theworkflows
- Then add action configuration file:
markdownlint.yml
- And finally add the filename:
badge.svg
Complete example:

Do yourself the favor of testing the URL before making commits containing it, it took me several attempts to get right.
Thanks to the nice supporter from GitHub who helped me out.