Prepare v0.5.6.0 release

We need to bump the version and update the changelog before cutting a release:)

Great...

Fwiw, link to the diff: https://gitlab.haskell.org/ghc/packages/array/-/compare/v0.5.5.0...release-v0.5.6.0?from_project_id=11&straight=false

added 1 commit

• 4440e869 - Some tidy-up changelog.md (please squash this commit)

Compare with previous version

Borrowed some github release message format and did a bit tidying up, if good please squash the commits. Looks good to me otherwise!

Awesome patch!

Little things I can do, thanks for your heavy lifting!

merged