git-gui: require git >= 2.36

git-gui: require git >= 2.36

git-gui since commit d6967022 explicitly requires version >= 1.5.0, and
this coded requirement has never been changed. But, since 0730a5a3a
git-gui actually requires git 2.36, providing 'git hook run.' git-gui
throws an error if that command is not supported.

So, let's update the requirement checking code to 2.36, and throw a more
useful error if this is not met.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>