relax ipywidgets (#9414) (#9442)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit 247c298)

Co-authored-by: Takashi Imamichi <31178928+t-imamichi@users.noreply.github.com>

requirements-dev.txt

@@ -3,7 +3,7 @@ hypothesis>=4.24.3
 python-constraint>=1.4
 ipython<7.22.0
 ipykernel<5.5.2
-ipywidgets>=7.3.0,<8.0.3
+ipywidgets>=7.3.0
 jupyter
 matplotlib>=3.3
 pillow>=4.2.1