Draft: Fix for #1066851.

I'm a little bit unsure about using "Depends: ${shlibs:Depends}" instead of "Depends: libreadline8". There is no binary / library in the resulting deb package, which uses the libreadline8 package, hence dh_gencontrol complains:

dpkg-gencontrol: warning: Depends field of package raku-readline: substitution variable ${shlibs:Depends} used, but is not defined

I guess the Dep on libreadline8 is completely useless too. If you think it is needed, please replace it by libreadline8t64.