pavucontrol-qt: add missing qtsvg dependency

For qt6, `qtsvg` needs to be explicitly installed for the icons to work
properly.

(cherry picked from commit bee9f56168)

pkgs/desktops/lxqt/pavucontrol-qt/default.nix

@@ -7,6 +7,7 @@
   lxqt-build-tools,
   pkg-config,
   qtbase,
+  qtsvg,
   qttools,
   qtwayland,
   wrapQtAppsHook,
@@ -35,6 +36,7 @@ stdenv.mkDerivation rec {
   buildInputs = [
     libpulseaudio
     qtbase
+    qtsvg
     qtwayland
   ];