mock-core-configs-39.3 switched the package manager for Fedora 40 to dnf5
https://fedoraproject.org/wiki/Changes/BuildWithDNF5
dnf5 builddep cannot handle BuildRequires with square brackets,
e.g. with Python extras, leading to errors like:
No match for argument: python3dist(setuptools-scm[toml]) >= 5
No match for argument: python3dist(raven[flask])
No match for argument: python3dist(ini2toml[lite]) >= 0.9
This is reported: https://github.com/rpm-software-management/dnf5/issues/1084
Until it is fixed, we explicitly use the "dnf" (i.e. DNF 4) package manager in mock,
even on Fedora 40+.
That way, if a package (such as python-tox) uses it,
the patches in dist-git are available.
In the future, it also allows us to add patches without URLs to our tested spec files.
Related: rhbz#2168193
