cmd_rename_workspace: always call con_focus

cmd_rename_workspace: always call con_focus

This was introduced in 252db3b8c (#3245). That commit moved the
con_activate line inside the loop, meaning it wouldn't always be called.

When the mouse moved after a rename with focus_follows_mouse enabled,
check_crossing_screen_boundary (src/handlers.c:111) called
con_descend_focused that used the wrong focus order.

I also change con_activate to con_focus since we don't really want to
raise floating containers there.

Fixes #3325