Support hasql 1.9

[kokobd]

Closes #370

[TeofilC]

Thanks! Have you tested this works correctly?

Could you also add a changelog entry using https://scriv.readthedocs.io/en/latest/

And make the language pragma consistent with the others.

I think otherwise this should be good to merge.

[kokobd]

1. I tested in these environments, each with a fixed hasql constraint in cabal.project of 1.8.1.4 / 1.9.1.2:
   • GHCup provided GHC 9.8.4 and 9.6.7, on aarch64-darwin
   • nix build .#checks.aarch64-darwin.tests
   • nix build .#checks.x86_64-linux.tests
2. The changelog is added and the language pragma issue is fixed.
3. I also made some nix related updates (these are not mentioned in changelog since they won't affect the released package):
   • I run nix flake update because the existing flake.lock was updated 22 months ago, which makes it impossible for nix users to test against hasql 1.9.
   • In flake.nix I changed it to use eachDefaultSystem so Mac users can enter the development shell. CI won't be able to run nix flake check because nix flake check wants to run the tests of all architectures on the same machine. I updated the CI to run nix build .#checks.x86_64-linux.tests instead.

[TeofilC]

Thanks!

[kokobd]

Hi @TeofilC the GitHub Actions workflow requires approval.