fix: put linux high dpi icons in the correct dir (#4281)

.changes/linux-icon-high-dpi.md

@@ -0,0 +1,6 @@
+---
+"tauri-bundler": patch
+---
+
+On Linux, high-dpi icons are now placed in the correct directory
+and should be recognized by the desktop environment.

tooling/bundler/src/bundle/linux/debian.rs

@@ -276,7 +276,7 @@ fn generate_icon_files(settings: &Settings, data_dir: &Path) -> crate::Result<BT
       "{}x{}{}/apps/{}.png",
       width,
       height,
-      if is_high_density { "@2x" } else { "" },
+      if is_high_density { "@2" } else { "" },
       settings.main_binary_name()
     ))
   };