Zeal Installation error

[hyosunko]

During the zeal doc installation, got the following error
brew install --HEAD zeal

❯ brew install --HEAD zeal
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 1 tap (homebrew/cask-versions).
==> Updated Casks
Updated 1 cask.

==> Installing zeal from markwu/personal
==> Cloning https://github.com/zealdocs/zeal.git
Updating /Users/hyosunko/Library/Caches/Homebrew/zeal--git
==> Checking out branch master
Already on 'master'
Your branch is up to date with 'origin/master'.
HEAD is now at d3c5521 build(appimage): pin appimage-builder to v0.8.3 (#1318)
==> git fetch --tags
==> git fetch --prune --unshallow
Last 15 lines from /Users/hyosunko/Library/Logs/Homebrew/zeal/02.git:
2021-06-19 11:58:56 -0700

git fetch --prune --unshallow

fatal: --unshallow on a complete repository does not make sense

If reporting this issue please do so at (not Homebrew/brew or Homebrew/core):
https://github.com/markwu/homebrew-personal/issues

These open issues may also help:
Is the complete Xcode needed to compile zeal? #4
Please create pull requests instead of asking for help on Homebrew's GitHub,
Twitter or any other official channels.

Manual installation was working fine though.