Bump ouroboros-consensus-diffusion

[bolt12]

• Bump ouroboros-consensus-diffusion 0.12
• Added entry for cardano-api 8.39.3 release.

Changelog

- description: |
    Bump ouroboros-consensus-diffusion 0.12
# 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
  # - improvement    # QoL changes e.g. refactoring
  # - 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

See #487 (comment)

[carbolymer]

Can you put this at the top? We would like to keep changelog in reverse chronological order.

[carbolymer]

can you bump hackage here as well:

nix flake update haskellNix/hackage

[bolt12]

done!