[ci] Enable testing builds on Fedora infrastructure

[bkmgit]

trafficstars

Additional tests that will make distributing RPMs easier.

To get it to work, someone with commit access will need to agree to make a Fedora account at: https://accounts.fedoraproject.org/

and agree to Fedora Code of Conduct, then follow the steps at:

http://packit.dev/docs/guide#1-set-up-packit-integration

The patch has changes in https://github.com/OpenCilk/opencilk-project/pull/343

It is possible to use specific commits for cheetah and productivity-tools