examples/Atreus2: Let TG(UPPER) go back to QWERTY from UPPER

To activate the `Upper` layer, one has to press `Fun+Esc`, and layers get locked
to `Upper`. To go back to base, one would need to press `Fun`, while the `Upper`
key itself is disabled.

For the sake of laziness, this little change turns that disabled key on the
`Upper` layer into the same macro key as `Fun`, so hitting the same position
again will get us back to the QWERTY layer.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

examples/Devices/Technomancy/Atreus2/Atreus2.ino

@@ -85,7 +85,7 @@ KEYMAPS(
        Key_Insert ,Key_Home                 ,Key_UpArrow   ,Key_End        ,Key_PageUp
       ,Key_Delete ,Key_LeftArrow            ,Key_DownArrow ,Key_RightArrow ,Key_PageDown
       ,XXX        ,Consumer_VolumeIncrement ,XXX           ,XXX            ,___ ,___
-      ,XXX        ,Consumer_VolumeDecrement ,___           ,___            ,___  ,___
+      ,M(QWERTY)  ,Consumer_VolumeDecrement ,___           ,___            ,___ ,___
 
                 ,Key_UpArrow   ,Key_F7 ,Key_F8          ,Key_F9         ,Key_F10
                 ,Key_DownArrow ,Key_F4 ,Key_F5          ,Key_F6         ,Key_F11