unpack_strategy/zip: allow unzip formula to be used

[Bo98]

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This is necessary for some Linux systems where there is no system unzip.

[BrewTestBot]

Review period skipped due to critical label.

[MikeMcQuaid]

Some comments, not blocking, nice work!

[MikeMcQuaid]

What happens if there's no system unzip and this is nil?

[Bo98]

PATH.new ignores nil so it'll just use ENV["PATH"].

[Bo98]

Oh misread your question. The command will fail to execute if there's no system unzip and this is nil (as it did before - so no change here). But this really should only be nil if homebrew-core is not installed, and I imagine there are many other issues in that case. All the other unpack strategies will actually error since they don't have a FormulaUnavailableError check (we do here because it's needed for the rspec tests).

If there's a different way we want to handle this, I think it should be done in a change applying to all unpack strategies, for consistency.

[MikeMcQuaid]

Gotcha, that all seems fine to me then 👍🏻