script/buildcontainer-setup: fix package install on debian trixie

script/buildcontainer-setup: fix package install on debian trixie

Debian removed software-properties-common from the archive in trixie,
so the flat apt-get install list fails there. The package was only
needed to provide add-apt-repository for llvm.sh, which installs
clang-19 from apt.llvm.org. Trixie ships clang-19 natively, so install
it from the distro instead; run-make.sh's prepare() then finds clang-19
and skips llvm.sh entirely. Ubuntu and older Debian releases still have
software-properties-common and keep the previous behavior.

Fixes: https://tracker.ceph.com/issues/78111
Signed-off-by: David Galloway <david.galloway@ibm.com>