feat(Cabal, cabal-install): Remove useless OptArg default argument

[zlonast]

This parameter is never used.

---

Template B: This PR does not modify behaviour or interface

E.g. the PR only touches documentation or tests, does refactorings, etc.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[jappeace]

Thanks

I guess those values were never used

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-08-23 12:59 UTC · Rule: default · triggered by rule Put pull requests in the rebase+merge queue
• ✅ Checks passed · on draft merge queue: checking master (2906373) and #12199 together #12259
• ✅ Merged — 2026-08-23 15:03 UTC · at bd55228c2264ea5f9269cd4367bab227c069624b · merge

This pull request spent 2 hours 4 minutes 42 seconds in the queue, including 1 hour 52 minutes 49 seconds running CI.

Required conditions to merge

• #review-threads-unresolved = 0 [🛡 GitHub branch protection]
  • feat(Cabal, cabal-install): Remove useless OptArg default argument #12199
• github-review-approved [🛡 GitHub branch protection]
  • feat(Cabal, cabal-install): Remove useless OptArg default argument #12199
• any of [🛡 GitHub branch protection]:
  • check-success = Doctest Cabal
  • check-neutral = Doctest Cabal
  • check-skipped = Doctest Cabal
• any of [🛡 GitHub branch protection]:
  • check-success = Meta checks
  • check-neutral = Meta checks
  • check-skipped = Meta checks
• any of [🛡 GitHub branch protection]:
  • check-success = docs/readthedocs.org:cabal
  • check-neutral = docs/readthedocs.org:cabal
  • check-skipped = docs/readthedocs.org:cabal
• any of [🛡 GitHub branch protection]:
  • check-success = Validate post job
  • check-neutral = Validate post job
  • check-skipped = Validate post job
• any of [🛡 GitHub branch protection]:
  • check-success = fourmolu
  • check-neutral = fourmolu
  • check-skipped = fourmolu
• any of [🛡 GitHub branch protection]:
  • check-success = hlint
  • check-neutral = hlint
  • check-skipped = hlint
• any of [🛡 GitHub branch protection]:
  • check-success = Bootstrap post job
  • check-neutral = Bootstrap post job
  • check-skipped = Bootstrap post job
• any of [🛡 GitHub branch protection]:
  • check-success = whitespace
  • check-neutral = whitespace
  • check-skipped = whitespace
• any of [🛡 GitHub branch protection]:
  • check-success = Check sdist post job
  • check-neutral = Check sdist post job
  • check-skipped = Check sdist post job
• any of [🛡 GitHub branch protection]:
  • check-success = Changelogs
  • check-neutral = Changelogs
  • check-skipped = Changelogs