fix: add Signed-By fields to apt sources

[mmstick]

In addition to pop-os/default-settings#175

[jacobgkau]

This failed to build for Noble. It's merging into master, which is successfully built for Noble right now. That seems like a problem, but I don't see what would be causing it-- do we know why that happened? (The Jenkins log is expired already.)

[jacobgkau]

I got this failure when trying to build locally on a Noble system:

Logs

   Compiling apt-cmd v0.5.0
The following warnings were emitted during compilation:

warning: gtk-sys@0.15.3:

error: failed to run custom build command for `gtk-sys v0.15.3`

Caused by:
  process didn't exit successfully: `/home/system76/upgrade/target/release/build/gtk-sys-14dfdd96381f7076/build-script-build` (exit status: 1)
  --- stdout
  cargo:rerun-if-env-changed=GTK+_3.0_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
  cargo:warning=
  pkg-config exited with status code 1
  > PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 pkg-config --libs --cflags gtk+-3.0 gtk+-3.0 >= 3.22

  The system library `gtk+-3.0` required by crate `gtk-sys` was not found.
  The file `gtk+-3.0.pc` needs to be installed and the PKG_CONFIG_PATH environment variable must contain its parent directory.
  The PKG_CONFIG_PATH environment variable is not set.

  HINT: if you have installed the library, try setting PKG_CONFIG_PATH to the directory containing `gtk+-3.0.pc`.

warning: build failed, waiting for other jobs to finish...
make[2]: *** [Makefile:77: target/release/libpop_upgrade_gtk.so] Error 101
make[2]: Leaving directory '/home/system76/upgrade'
make[1]: *** [debian/rules:18: override_dh_auto_build] Error 2
make[1]: Leaving directory '/home/system76/upgrade'
make: *** [debian/rules:7: build] Error 2
dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2

I ran sudo apt build-dep pop-upgrade before attempting this. libgtk-3-dev is already installed. Not sure what the correct package name is to provide what's missing, assuming it's a missing dependency.