gio/tests: Guard variable that is used on windows only builds

gio/src/subclass/application.rs

@@ -416,16 +416,17 @@ mod tests {
         impl ObjectImpl for SimpleApplication {}
 
         impl ApplicationImpl for SimpleApplication {
-            fn command_line(&self, cmd_line: &crate::ApplicationCommandLine) -> ExitCode {
-                let arguments = cmd_line.arguments();
-
-                // NOTE: on windows argc and argv are ignored, even if the arguments
-                // were passed explicitly.
-                //
-                // Source: https://gitlab.gnome.org/GNOME/glib/-/blob/e64a93269d09302d7a4facbc164b7fe9c2ad0836/gio/gapplication.c#L2513-2515
+            fn command_line(&self, _cmd_line: &crate::ApplicationCommandLine) -> ExitCode {
                 #[cfg(not(target_os = "windows"))]
-                assert_eq!(arguments.to_vec(), &["--global-1", "--global-2"]);
-
+                {
+                    let arguments = _cmd_line.arguments();
+
+                    // NOTE: on windows argc and argv are ignored, even if the arguments
+                    // were passed explicitly.
+                    //
+                    // Source: https://gitlab.gnome.org/GNOME/glib/-/blob/e64a93269d09302d7a4facbc164b7fe9c2ad0836/gio/gapplication.c#L2513-2515
+                    assert_eq!(arguments.to_vec(), &["--global-1", "--global-2"]);
+                };
                 EXIT_STATUS.into()
             }