update nix files for ghc-9.6

[imalsogreg]

Bumps to the nix files (and comments in cabal.project that support nix), for ghc-9.6.

[greghale@michelangelo:~/code/pact]$ nix develop
[greghale@michelangelo:~/code/pact]$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.6.2

Check	MacOS	NixOS
ghc fetched from cache	✓	✓
pact repl works	✓	✓

PR checklist:

• [n/a] Test coverage for the proposed changes
• [n/a] PR description contains example output from repl interaction or a snippet from unit test output
• [n/a] Documentation has been updated if new natives or FV properties have been added. To generate new documentation, issue cabal run tests. If they pass locally, docs are generated.
• [n/a] Any changes that could be relevant to users have been recorded in the changelog
• [n/a] In case of changes to the Pact trace output (pact -t), make sure pact-lsp is in sync.

Additionally, please justify why you should or should not do the following:

• [n/a] Confirm replay/back compat: pact's nix files aren't used downstream in replay
• [n/a] Benchmark regressions: pact's nix files aren't used for official releases, where regressions would be a problem
• [n/a] (For Kadena engineers) Run integration-tests against a Chainweb built with this version of Pact. pact's nix files aren't used by chainweb

[rsoeldner]

👍