Fix missing zlib in WASM nix shell

[carbolymer]

Changelog

- description: |
    Fix missing zlib in WASM nix shell
# 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...
  projects:
  - cardano-wasm

Context

For some reason haskell package digest was trying to find zlib in pkg-config output, which does not succeed on WASM platform. We can tell it to not use pkg-config for that: https://hackage.haskell.org/package/digest-0.0.2.1

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

[palas]

If it compiles...
Thank you 🙂