This was merged to the 3.9.x branch as of https://github.com/puppetlabs/facter/commit/24c48d26c29ce1691a5e724030c210581a474d91, and should get merged up to master soon.
The changes I made should fix facter os detection for sles, sled, and opensuse-leap. Agent work for SLES 15 is currently ongoing.
Scott Garman, when you have a chance, could you please add release notes (or indicate that they're not needed)? Thanks!