Bug#1101905: libqwt-qt5-6.3 and libqwt-qt6-6.3 have an undeclared file conflict

[Drew Parsons]

Source: qwt
Followup-For: Bug #1101905

This bug was fixed for libqwt-qt6-6.3 in 6.3.0-2, but I think the
problem is still there in libqwt-qt5-6.3
(/usr/lib/x86_64-linux-gnu/libqwt-qt5.so.6 is still provided)