Add two more packages for Debian/Ubuntu

If libtinfo5 isn't installed, then installation fails with a message like this:
/home/ubuntu/.ghcup/ghc/8.6.5/lib/ghc-8.6.5/bin/ghc-pkg: error while loading shared libraries: libtinfo.so.5: cannot open shared object file: No such file or directory

If xz-utils isn't installed, then installation fails with a message like this:
Following commands are required, but missing, please install:  xz

.requirements/ghc/ubuntu

-build-essential curl libgmp-dev libffi-dev libncurses-dev
+build-essential curl libgmp-dev libffi-dev libncurses-dev libtinfo5 xz-utils