Fix terraform extract

[cpc-camarj]

On Windows runners, extracting the downloaded CLI zip file was failing because the file didn't have a .zip extension. This PR attempts to solve the problem by adding the extension to the downloaded file before extraction.

(fixes #186)

[hashicorp-cla]

All committers have signed the CLA.

[cpc-camarj]

I identified that I had set a variable to be constant rather than mutable. added a commit to fix that. Validated within a private GitHub workflow this morning that it functions as expected.

(Well, it happens to be morning where I am right now)

[jpogran]

Thanks for the contribution @cpc-camarj! I'll be able to review this tomorrow, but it looks good so far.

[jpogran]

Apologies for the delay in merging. Thank you!

[github-actions]

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