Check in CI if changelogs need a bump

[Lucsanszky]

Description

This PR adds a simple safeguard to CI that checks if CHANGELOGs need bumping, using our existing bump-changelogs.sh script.

Checklist

• Commits in meaningful sequence and with useful messages.
• Tests added or updated when needed.
• CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• Code formatted (use scripts/fourmolize.sh).
• Cabal files formatted (use scripts/cabal-format.sh).
• CDDL files are up to date (use scripts/gen-cddl.sh)
• hie.yaml updated (use scripts/gen-hie.sh).
• Self-reviewed the diff.

[Lucsanszky]

Here's a demonstration of how this will look in action: https://github.com/IntersectMBO/cardano-ledger/actions/runs/18292660765/job/52083448456

[teodanciu]

Why this change?

[Lucsanszky]

It didn't work on CI via SSH, probably because the key is not configured their, so reverting to HTTPS.

[neilmayhew]

You can alternatively fetch a tarball using the archive URL.

However, even better I think is to use the CHaP index file rather than the repo. Although the git repo and the package repo should never be out of step, using the index guarantees that you see exactly what Cabal sees. It also avoids having to run a script to calculate the package list from the repo state.

You can see an example of doing this in a script I added to the CHaP git repo.

I think downloading the index file may also be a little faster because it's smaller than the whole repo.

[neilmayhew]

BTW, I couldn't comment on this in the review because the line isn't changed in this PR, but I think it would be better to use git ls-files here rather than find:

CABAL_FILES=$(find . -wholename '*/eras/*.cabal' -o -wholename '*/libs/*.cabal')

find will end up searching dist-newstyle and other ignored directories (to depth 1, at least) and will also pick up stray cabal files that haven't been added to git.

With git ls-files it would look like this:

CABAL_FILES=$(git ls-files 'eras/*.cabal' 'libs/*.cabal')

However, this also works and is simpler:

CABAL_FILES=$(git ls-files '*.cabal')

[lehins]

Removing this section is not correct. So, this change is here to test whether this new CI check works correctly or not, right?