Shellcheck check-cabal-files.sh

[smelc]

Changelog

- description: |
    Shellcheck check-cabal-files.sh
# 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

Follow-up of #734, making check-cabal-files.sh shellcheck-compliant and actually checking it in the CI (by removing it from the list of exceptions).

How to trust this PR

Execute ./scripts/ci/check-cabal.files.sh before and after this change and witness it outputs the same.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• Self-reviewed the diff