By: Greg Pfeil <greg@technomadic.org>
Use a path instead of a string for `callCabal2nix` This should filter out the other packages, speeding up Nix builds.
| Time to Start | Worker time | Duration | Time to finish | |
| Config | 19s | 5s | 5s | 24s |
| Eval | 23s | 53s | 53s | 1m16s |
| Build | 50s | 3m44s | 1m10s | 2m01s |
| Test | - | - | - | - |
| Deploy | - | - | - | - |
| Suite | 19s | 4m43s | 1m41s | 2m01s |