Remove branch input workarounds now that `job_workflow_sha` works properly

Until recently the `github.job_workflow_sha` value wasn't set correctly in jobs that use a reusable workflow:
- https://github.com/actions/runner/issues/2417

This meant we had to add some workarounds in the actions in this repo:
https://github.com/heroku/languages-github-actions/blob/2652b059e05ccafc7c747973813d8bc6d6b1bc5c/.github/actions/install-languages-cli/action.yml#L5-L12

See also:
https://github.com/heroku/languages-github-actions/issues/106#issuecomment-1673238113

Now that `job_workflow_sha` is fixed, we should switch to that and remove the workarounds :-)

Start with .github/actions/install-languages-cli/action.yml, especially lines 5–12, and review the related workaround context in issue #106. Check the repository’s actions for similar branch-input workarounds, then switch them to github.job_workflow_sha and remove the obsolete inputs; done means the actions no longer need the workaround while continuing to work with reusable workflows.

Written by the indexing model from the issue text.