Formula-Cookbook: update for Homebrew v4

[unitof]

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The Formula Cookbook includes some instructions which no longer work out of the box on Homebrew ≥4.0.0; this PR aims to update the documentation and correct the commands as necessary for local formulae development.

I don't believe any tests are necessary, but this is my first time contributing to docs so I could be wrong.

Fixes #14757

[request-info]

Please provide a better issue/pull request title and/or description!

[gromgit]

Suggest setting HOMEBREW_NO_INSTALL_FROM_API to 1 instead of 0, to be consistent with the manpage:

Note that environment variables must have a value set to be detected. For example, run export HOMEBREW_NO_INSECURE_REDIRECT=1 rather than just export HOMEBREW_NO_INSECURE_REDIRECT.

[unitof]

Suggest setting HOMEBREW_NO_INSTALL_FROM_API to 1 instead of 0, to be consistent with the manpage:

Note that environment variables must have a value set to be detected. For example, run export HOMEBREW_NO_INSECURE_REDIRECT=1 rather than just export HOMEBREW_NO_INSECURE_REDIRECT.

🤦🏻 thanks!

[MikeMcQuaid]

Thanks for the PR! Looking good so far, some wording tweaks, feel free to push back on any you disagree with and we can talk about them more.

[peterldowns]

This PR helped me work around a problem I had when creating a new formula. Looks like someone else had the same problem too. Linking this here in case it helps others.

[Rylan12]

Thanks @unitof, this looks great and is a huge improvement!

[slonopotamus]

Directly related: #14757. Possibly even this PR fixes #14757.

[MikeMcQuaid]

Thanks so much for your repeated contribution and sponsorship! Without people like you submitting PRs we couldn't run this project. You rock, @unitof!