Fix conda release
There were a few issues with conda releases (they've been failing for a while now).
To fix this I had to:
- add the --single-version-externally-managed tag to the build stage (suggestion from [here](https://stackoverflow.com/a/64825075))
- set the python version of the conda build stage to 3.8 since 3.9 isn't supported
- sync the evrsion requirement of `huggingface_hub`

With these changes I'm working on uploading all missing versions until 1.6.2 to conda

EDIT: I managed to build and upload all missing versions until 1.6.2 to conda :)