chore(deps): update dependency imageio to v2.9.0 (#4241)

Author: renovate-bot

appengine/flexible/scipy/requirements.txt

@@ -1,6 +1,6 @@
 Flask==1.1.2
 gunicorn==20.0.4
-imageio==2.8.0
+imageio==2.9.0
 numpy==1.19.0
 pillow==7.2.0
 scipy==1.5.1