Raise an exception when `=` is used with short option

[j-mracek]

It prevents silently skipping the change in behavior between DNF4 and DNF5 Where -x=dnf excluded dnf but in DNF5 it excludes =dnf. Without the exception it would be hard to detect that something might work differently then expected.

Closes: https://github.com/rpm-software-management/dnf5/issues/1353