`delete-unmanaged` should detect squash and merged branches

[cinnamennen]

Overview

When a PR is merged I can run traverse and the branch that was merged in will be slid out. However delete-unmanaged will say unmerged to HEAD and prompt for confirmation.

Expected behavior/command output

delete-unmanaged should be able to tell that a branch has been squashed and merged.

Actual behavior/command output

It doesn't.

git and git machete versions

git --version 2.46.0

git-machete version 3.28.0