style: use string constants for refs/ paths
These were introduced in Dulwich 0.19.3, released in June 2018. We obtain most of these directly, but there's no constant for remotes, though, so we add our own.
This instance will be updated to Heptapod 18.6.0rc1 on 2025-12-08 between 11:00 and 12:00 UTC+1 (Europe/Paris)
These were introduced in Dulwich 0.19.3, released in June 2018. We obtain most of these directly, but there's no constant for remotes, though, so we add our own.