hotfix: drop bad pyyaml version (#5606)

* drop potetionaly bad version

* *

requirements.txt

@@ -4,7 +4,7 @@ numpy>=1.16.6
 torch>=1.3
 future>=0.17.1  # required for builtins in setup.py
 # pyyaml>=3.13
-PyYAML>=5.1  # OmegaConf requirement >=5.1
+PyYAML>=5.1, !=5.4.*  # OmegaConf requirement >=5.1
 tqdm>=4.41.0
 fsspec[http]>=0.8.1
 tensorboard>=2.2.0