deb: use variable expansion to support systemd unit dir changes

deb: use variable expansion to support systemd unit dir changes

Ubuntu changed the systemd unit directory location between releases:
- Jammy (22.04): /lib/systemd/system
- Noble (24.04): /usr/lib/systemd/system

To maintain compatibility across both versions, update .install files
to use brace expansion pattern {usr/,}lib/systemd/system/<service>.

This pattern works because dh_install uses bsd_glob() with GLOB_CSH
flags, which expands braces and matches files in both locations
depending on where CMakeLists.txt actually installed them.

Fixes installation issues when building packages on Noble while
maintaining backward compatibility with Jammy builds.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
(cherry picked from commit 04324fa1ac1916b7a3db7928b26d4660c099d35c)