libfplll soname bump

I will soon build libfplll 5.3.0 in Rawhide, which entails an soname
bump from to, even though abipkgdiff
reports no ABI changes. I will rebuild the dependent packages,
gap-pkg-float and python-fpylll. Note that linbox and Macaulay2 also
consume libfplll-static, but since there are no ABI changes, I'll
leave them to their next updates or the mass rebuild, whichever comes