Use official terraform-docs releases again

[mcdonnnj]

🗣 Description

This pull request restores using official terraform-docs releases in the build workflow. This resolves #165.

💭 Motivation and context

With the merge of my two feature branches into the terraform-docs repository and the new 0.22.0 release we can start using official releases again.

🧪 Testing

Automated tests pass.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.

[Copilot]

Pull request overview

This pull request updates the CI build workflow to use the upstream terraform-docs project again (via versioned installs) rather than building from a temporary fork/branch, resolving the earlier workaround tracked in issue #165.

Changes:

• Removed fork/branch environment variables used to clone a temporary terraform-docs fork.
• Replaced the clone+local build steps with a go install of terraform-docs at the version provided by setup-env.

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[jsf9k]

Doesn't this resolve #165? You should add that to the description so the issue gets closed.

[mcdonnnj]

Doesn't this resolve #165? You should add that to the description so the issue gets closed.

That was already mentioned in the description and linked.

[jsf9k]

Doesn't this resolve #165? You should add that to the description so the issue gets closed.

That was already mentioned in the description and linked.

Sorry, I somehow missed that. I usually put it in the motivation section.