Tests for Spaces requirements.txt upon push of new module

Upon merges we've sometimes had metrics Spaces break because of missing requirements which then need to be added to requirements.txt later.

Not sure what the best way to detect this is, though — sometimes it's not obvious because the requirement is wrapped in a library which has optional dependencies (e.g. [this](https://huggingface.co/spaces/evaluate-measurement/toxicity/blob/main/toxicity.py) one requires torch because it loads a torch classifier, but you wouldn't know it from the imports).