fix up CI:

add libhandy as dependency
change ubuntu actions environment
update nlohmann/json to latest release
add preprocessor checks

src/audio/devices.cpp

@@ -1,5 +1,11 @@
+#ifdef WITH_VOICE
+
+// clang-format off
+
 #include "devices.hpp"
 
+// clang-format on
+
 AudioDevices::AudioDevices()
     : m_playback(Gtk::ListStore::create(m_playback_columns)) {
 }
@@ -31,3 +37,4 @@ AudioDevices::PlaybackColumns::PlaybackColumns() {
     add(Name);
     add(DeviceID);
 }
+#endif

src/audio/devices.hpp

@@ -1,9 +1,14 @@
 #pragma once
+#ifdef WITH_VOICE
+
+// clang-format off
 
 #include <gtkmm/liststore.h>
 #include <miniaudio.h>
 #include <optional>
 
+// clang-format on
+
 class AudioDevices {
 public:
     AudioDevices();
@@ -24,3 +29,4 @@ private:
     PlaybackColumns m_playback_columns;
     Glib::RefPtr<Gtk::ListStore> m_playback;
 };
+#endif