fix readthedoc dependency error (sunlabuiuc#519)

Co-authored-by: John Wu <johnwu3@sunlab-work-01.cs.illinois.edu>

Author: jhnwu3

docs/requirements.txt

@@ -23,4 +23,5 @@ gspread==5.6.2
 google-cloud-storage==2.6.0
 oauth2client==4.1.3
 Jinja2==3.1.4
-flask==2.2.5
+flask==2.2.5
+pydantic