Formula-Cookbook: Recommend the in-use write_exec_script syntax

[issyl0]

• 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?
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• Have you successfully run brew tests with your changes locally?

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• The bin.write_exec_script Dir[libexec/"bin/*"] is used in core formulae, whereas the previously recommended syntax is not found at all. Let's make reality match the documentation.
• Part of https://github.com/orgs/Homebrew/projects/5?pane=issue&itemId=97021840.

[p-linnane]

Great catch!

[MikeMcQuaid]

Thanks @issyl0!