It depends if you’re trying to use the newer fast ai or the older one. It looks like you’re trying to run a notebook that relies on the older version. environment.yml doesn’t specify a version, and so it downloads the latest fastai. You can do something along the lines of pip install 'fastai<=0.7'. Or put that in the environment.yml and do a conda env update.
You’ll also need to get the right version of torchtext. See Google Colab-AttributeError: module ‘torch’ has no attribute ‘float32’