setuptools_scm: how to append "-alpha" to package version upon merge in gitflow?

My team uses:

• Gitflow: we have a main and a develop branch
• Semantic versioning per https://semver.org/
• setuptools_scm for our package version publishing

We would like to publish a bugfix version bump over the previous tag on main with some modification:

• Merges to develop: publish -alpha package
• Merges to main: publish -beta package

Here's an example:

1. Last tag on main: 1.2.3
2. Next merge to develop: 1.2.4-alpha
3. Next merge to develop: 1.2.4-alpha.1
4. Next merge to develop: 1.2.4-alpha.2
5. Finally a merge to main: 1.2.4-beta

...

Finally, a tag on main is manually made: 1.2.4

How can one accomplish stuff like this using setuptools_scm?

from setuptools_scm: how to append "-alpha" to package version upon merge in gitflow?