Pin protobuf version

Author: akihironitta

requirements/base.txt

@@ -3,6 +3,7 @@ torch>=1.8.*, <=1.11.0
 tqdm>=4.57.0, <=4.63.0
 PyYAML>=5.4, <=6.0
 fsspec[http]>=2021.05.0, !=2021.06.0, <=2022.2.0
+protobuf<4.21.0
 tensorboard>=2.2.0, <2.10.0
 torchmetrics>=0.4.1, <=0.7.2
 pyDeprecate>=0.3.1, <=0.3.2