Rename `master` branch to `main`

[m4olivei]

Rationale

See https://architecture.lullabot.com/adr/20220511-use-inclusive-language/

References

• https://github.com/github/renaming#rename-existing
• https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-branches-in-your-repository/renaming-a-branch
• https://grrr.tech/posts/2022/master-to-main/

To do:

• [x] Rename branch via Github UI
• [x] Rename references to master on Github actions to main after the change
• [x] Rename references to master in raw code links througout the codebase, eg. this one
• [x] Update local clone(s) as necessary