CI: check if packages in _pmb_recommends exist
Currently CI doesn't check if packages in _pmb_recommends exist, which may result in issues like !1466 (merged), where postmarketos-ui-plasma-desktop could not be installed.
Currently CI doesn't check if packages in _pmb_recommends exist, which may result in issues like !1466 (merged), where postmarketos-ui-plasma-desktop could not be installed.