GitHub’s own "Edit readme" link points to 404 on tag pages #2997

1. Visit a repo you own
2. Open the latest tag (like https://github.com/sindresorhus/refined-github/tree/20.4.9)
3. Click edit button on top right of readme
4. See 404 at /$USER/$REPO/edit/$TAG/readme.md

This button is added by GitHub, it's their own bug.

On tag pages, that link should edit the readme on the default branch.

The edit-readme feature should be extended to also fix this GitHub bug.

Previously discussed in https://github.com/sindresorhus/refined-github/issues/2982