Simplify GHAs using nix, update nix shell haskell tools

[carbolymer]

Changelog

- description: |
    Simplify GHA using nix, update nix shell haskell tools
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
   - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

Simplify GHAs using nix, update nix shell haskell tools:

• HLS 2.9
• ghcid 0.8.9
• fourmolu 0.17

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Jimbo4350]

Where is the CABAL_GILD_VERSION env variable defined?

[carbolymer]

Good catch

[smelc]

Suggested change

	echo "cabal-gild version: ${{env.CABAL_GILD_VERSION}}"
	echo "cabal-gild version: $(cabal-gild --version)"

[carbolymer]

Good catch

[smelc]

Nice 💯