title: I can't run `git gui` on macOs Big Sur
body: <p>When I run <code>git gui</code> on Mac Big Sur . This is what happen :</p>
  <pre><code>Mac OS X 10.100 or later required !
  error: git-gui died of signal 6
  </code></pre>
  <p>I also install <code>xcode 12 beta 3</code> and <code>xcodebuild -version</code> stays <code>Xcode 11.6</code> .</p>
  <p>How can I solve those problems ?</p>