You can split your template however you choose. Here is an example for a KDE application:
For example, all applications in KDE GitLab CI are built as Flatpak from the same template:
We could certainly do the same for RPM packaging.
Forgejo Actions are similar to GitHub Actions (Forgejo Actions user guide | Forgejo – Beyond coding. We forge.) and we could indeed create a set of Actions that do the RPM packaging and testing in a similar fashion to what’s done today in Zuul/Testing Farm.
Or we could also plug the existing CI (Zuul/Testing Farm) to it to get up to speed quicker.
I regularly use both GitLab CI & GitHub Actions and they both have their advantages and downsides.