[Bug] Invalid formula. Undefined method `on_arm'

[pshabunia]

Describe the Bug

brew install qmk/qmk/qmk and brew tap qmk/qmk run into an error

> brew tap qmk/qmk                              
Error:
  homebrew-core is a shallow clone.
To `brew update`, first run:
  git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow
This command may take a few minutes to run due to the large size of the repository.
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!
==> Tapping qmk/qmk
Cloning into '/usr/local/Homebrew/Library/Taps/qmk/homebrew-qmk'...
remote: Enumerating objects: 527, done.
remote: Counting objects: 100% (87/87), done.
remote: Compressing objects: 100% (43/43), done.
remote: Total 527 (delta 47), reused 78 (delta 41), pack-reused 440 (from 1)
Receiving objects: 100% (527/527), 88.89 KiB | 0 bytes/s, done.
Resolving deltas: 100% (310/310), done.
Checking connectivity... done.
Error: Invalid formula: /usr/local/Homebrew/Library/Taps/qmk/homebrew-qmk/Formula/qmk.rb
qmk: undefined method `on_arm' for Formulary::FormulaNamespace557ef0844d1f67c9536fc3f101472437::Qmk:Class
Error: Cannot tap qmk/qmk: invalid syntax in tap!

Additional Context?

It never worked via brew. I used to run QMK in a docker container, then I figured how to install it with a pip (port install dfu-utils avrdude avr-binutils avr-gcc avr-libc + pip install qmk) but it all was supposed to be a temporary solution. I want to make it work via brew.

[fauxpark]

What version of macOS are you on? Did you make sure to update Homebrew first?

[pshabunia]

Good point, @fauxpark

The problem disappeared after updates to homebrew.