Bring Cabal files in sync with Flaky template (#4) Notably, this uses `GHC2021` as the `default-language` and fixes the `setup-depends` bounds for Cabal (which would have prevented publishing to Hackage).
| Time to Start | Worker time | Duration | Time to finish | |
| Config | 0s | 1s | 1s | 1s |
| Eval | 1s | 1s | 1s | 2s |
| Build | 2s | 14s | 16s | 19s |
| Suite | 0s | 16s | 19s | 19s |