tfenv: fix patch url (rollup) + improve test

[gromgit]

In support of Homebrew/brew#8075

Also make test match a specific version tag, instead of spewing the entire version list for visual confirmation.

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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