Pin flask < 3.x for flask sqlalchemy tests (#412)

Author: srprash

tox.ini

@@ -74,7 +74,7 @@ deps =
 
     ext-flask: flask >= 0.10
 
-    ext-flask_sqlalchemy: flask >= 0.10
+    ext-flask_sqlalchemy: flask >= 0.10,<3.0.0
     ext-flask_sqlalchemy: Flask-SQLAlchemy <= 2.5.1
     ext-flask_sqlalchemy: sqlalchemy >=1.0.0,<2.0.0