incompatible protobuf versions for mediapipe and rasa

[sthoduka]

The latest version of rasa requires protobuf >=4.23.3 (see here) The latest version of mediapipe requires protobuf < 4 (see here)

For now we've downgraded rasa to 3.6.1 which has protobuf requirement of >=3.9.2

@MannavaVivek @NadaAweaa