Fix typo (backport #9770)

[mergify]

Missing full stop.

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• Patches conform to the coding conventions.
• [ ] Any changes that could be relevant to users have been recorded in the changelog. not present in 3.10, so I would say a changelog entry is not needed.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• [ ] Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!) one-liner, not needed

  ---

  This is an automatic backport of pull request Fix typo #9770 done by Mergify.

[mergify]

Cherry-pick of 6bad26a has failed:

On branch mergify/bp/3.12/pr-9770
Your branch is up to date with 'origin/3.12'.

You are currently cherry-picking commit 6bad26a2d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   cabal-install/src/Distribution/Client/Setup.hs

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[ulysses4ever]

This one is not needed. 3.12 had a backport of #9583 (see #9893), and it supersedes this one.