workaround to make inspector tests pass without blocking window
workaround to make inspector tests pass without blocking window

the root cause of the issue hasn't been identified but:

- the render() call blocks, apparently waiting for a window flip event
- it's been introduced by commit be1ce, which prevents adding a widget
  to a window if it already has a parent.
- checking in inspector if it already has a parent before adding it to
  window doesn't seem to fix the issue.

see #5645 ##5646 #5658

kivy/kivy,akshayaurora/kivy,rnixx/kivy,LogicalDash/kivy,kivy/kivy,matham/kivy,matham/kivy,rnixx/kivy,inclement/kivy,matham/kivy,akshayaurora/kivy,LogicalDash/kivy,LogicalDash/kivy,kivy/kivy,rnixx/kivy,akshayaurora/kivy,inclement/kivy,inclement/kivy,LogicalDash/kivy,matham/kivy