Fix floating window width increase when moving to workspace

* exwm-workspace.el (exwm-workspace-move-window): Deduct 1 pixel from
`frame-pixel-width' of `old-frame' when moving a floating window to another
workspace.  This prevents the floating window from growing in width over
repeated moves.

exwm-workspace.el

@@ -938,7 +938,7 @@ INDEX must not exceed the current number of workspaces."
               (set-frame-parameter new-frame 'exwm-container container)
               (make-frame-invisible new-frame)
               (set-frame-size new-frame
-                              (frame-pixel-width old-frame)
+                              (- (frame-pixel-width old-frame) 1)
                               (frame-pixel-height old-frame)
                               t)
               (xcb:+request exwm--connection