Userland: Cast unused BackgroundAction::construct() results to void

User code does not need to keep this alive, so casting to void is safe.
But maybe a bit weird.

Userland/Applications/Assistant/Providers.cpp

@@ -163,7 +163,7 @@ void FileProvider::build_filesystem_cache()
     m_building_cache = true;
     m_work_queue.enqueue("/");
 
-    Threading::BackgroundAction<int>::construct(
+    (void)Threading::BackgroundAction<int>::construct(
         [this](auto&) {
             String slash = "/";
             auto timer = Core::ElapsedTimer::start_new();

Userland/Applications/DisplaySettings/MonitorWidget.cpp

@@ -30,7 +30,7 @@ bool MonitorWidget::set_wallpaper(String path)
     if (!is_different_to_current_wallpaper_path(path))
         return false;
 
-    Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
+    (void)Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
         [path](auto&) -> ErrorOr<NonnullRefPtr<Gfx::Bitmap>> {
             if (path.is_empty())
                 return Error::from_errno(ENOENT);

Userland/Applications/SystemMonitor/ThreadStackWidget.cpp

@@ -113,7 +113,7 @@ private:
 
 void ThreadStackWidget::refresh()
 {
-    Threading::BackgroundAction<Vector<Symbolication::Symbol>>::construct(
+    (void)Threading::BackgroundAction<Vector<Symbolication::Symbol>>::construct(
         [pid = m_pid, tid = m_tid](auto&) {
             return Symbolication::symbolicate_thread(pid, tid, Symbolication::IncludeSourcePosition::No);
         },

Userland/DevTools/HackStudio/LanguageServers/Cpp/main.cpp

@@ -37,7 +37,7 @@ ErrorOr<int> mode_server()
     TRY(Core::System::pledge("stdio unix recvfd rpath"));
 
     auto socket = TRY(Core::LocalSocket::take_over_accepted_socket_from_system_server());
-    IPC::new_client_connection<LanguageServers::Cpp::ClientConnection>(move(socket), 1);
+    (void)IPC::new_client_connection<LanguageServers::Cpp::ClientConnection>(move(socket), 1);
 
     TRY(Core::System::pledge("stdio recvfd rpath"));
     TRY(Core::System::unveil("/usr/include", "r"));

Userland/DevTools/HackStudio/LanguageServers/Shell/main.cpp

@@ -17,7 +17,7 @@ ErrorOr<int> serenity_main(Main::Arguments)
     TRY(Core::System::pledge("stdio unix rpath recvfd"));
 
     auto socket = TRY(Core::LocalSocket::take_over_accepted_socket_from_system_server());
-    IPC::new_client_connection<LanguageServers::Shell::ClientConnection>(move(socket), 1);
+    (void)IPC::new_client_connection<LanguageServers::Shell::ClientConnection>(move(socket), 1);
     TRY(Core::System::pledge("stdio rpath recvfd"));
     TRY(Core::System::unveil("/etc/passwd", "r"));
 

Userland/Libraries/LibGUI/FileSystemModel.cpp

@@ -649,7 +649,7 @@ bool FileSystemModel::fetch_thumbnail_for(Node const& node)
 
     auto weak_this = make_weak_ptr();
 
-    Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
+    (void)Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
         [path](auto&) {
             return render_thumbnail(path);
         },

Userland/Services/WindowServer/Compositor.cpp

@@ -807,7 +807,7 @@ bool Compositor::set_wallpaper_mode(const String& mode)
 
 bool Compositor::set_wallpaper(const String& path, Function<void(bool)>&& callback)
 {
-    Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
+    (void)Threading::BackgroundAction<ErrorOr<NonnullRefPtr<Gfx::Bitmap>>>::construct(
         [path](auto&) {
             return Gfx::Bitmap::try_load_from_file(path);
         },