cmd/tap: add missing require

[p-linnane]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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Fixes https://github.com/orgs/Homebrew/discussions/5492

[p-linnane]

brew update-test is broken for me locally, even on the current stable tag.

[Bo98]

Uh oh that doesn't sound good - will check