brew.sh: set HOMEBREW_FORCE_HOMEBREW_ON_LINUX when core repo is homeb…

[iMichka]

…rew-core

See Homebrew/install#571

When the install script sets as https://github.com/Homebrew/homebrew-core,
we need to use the homebrew-core bottle domain, and correctly set
the HOMEBREW_CORE_DEFAULT_GIT_REMOTE below.

This also fixes the brew doctor issue for new homebrew-core Linux installations

Warning: Suspicious https://github.com/Homebrew/linuxbrew-core git origin remote found.
The current git origin is:
https://github.com/Homebrew/homebrew-core

With a non-standard origin, Homebrew won't update properly.
You can solve this by setting the origin remote:
git -C "/home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core" remote set-url origin https://github.com/Homebrew/linuxbrew-core

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• 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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[BrewTestBot]

Review period will end on 2021-08-31 at 00:00:00 UTC.

[Bo98]

The check here would also need adjusting:

brew/Library/Homebrew/extend/os/linux/tap.rb

Line 8 in 3476ca7

@full_name = "Homebrew/linuxbrew-core" unless Homebrew::EnvConfig.force_homebrew_on_linux?

[BrewTestBot]

Review period ended.

[MikeMcQuaid]

Looks good once @Bo98's comment is addressed.

[MikeMcQuaid]

Thanks again @iMichka!