Use HOMEBREW_CURLRC in vendor-install

[clint-stripe]

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Following #15853, there is another place we call curl that can also make use of HOMEBREW_CURLRC to set --config. HOMEBREW_ARTIFACT_DOMAIN is used in line 48 here, so the change in Utils::Curl didn't have any effect.

I missed this because I didn't test installing Homebrew from scratch with this set 😅

[MikeMcQuaid]

Looks good, thanks again @clint-stripe!