The hack of using "secrets" to store per-repo settings was not working.
The main reason is that pull_request workflows don't have access to
secrets no matter what you do. So it was impossible to make this work
for settings like "ENABLE_SELF_HOSTED" for PR tests.
This change replaces that old hack with a new one. Now a repo owner must
create a "GitHub Environment" with the name of the setting they want to
enable. Currently supported values are "self_hosted", to add self-hosted
runners to the build/test matrix, and "debug", to start an SSH server
for debugging when a workflow fails.
Issue #1047 (CMake porting)
Joey Parrish