Downgrade protobuf from 3.20 to 3.19

```text
he conflict is caused by:
    The user requested protobuf==3.20.0
    wandb 0.12.17 depends on protobuf<4.0dev and >=3.12.0
    tensorflow 2.7.1 depends on protobuf>=3.9.2
    tensorflow-docs 0.0.0.dev0 depends on protobuf<3.20 and >=3.12.0
```