Fix pushing keyboard and mouse to the same stack level (#2636)

Author: csd4ni3l

arcade/application.py

@@ -314,7 +314,8 @@ def __init__(
 
             else:
                 self.mouse = pyglet.window.mouse.MouseStateHandler()
-                self.push_handlers(self.keyboard, self.mouse)
+                self.push_handlers(self.keyboard)
+                self.push_handlers(self.mouse)
         else:
             self.keyboard = None
             self.mouse = None