CI/CD: Add a scalafmt check to github actions

[matejcerny]

To prevent errors with Sonatype release, add a scalafmtAll step to github actions.

[geirolz]

Do we want a step that fails if the code isn't properly formatted ? Because scalafmtAll implies a commit

[matejcerny]

Sorry, you are right, it should be scalafmtCheckAll. Imho it's better to fail the whole pipeline rather than examine why the release does not work.