fix: use pyyaml instead of pyaml

As python is python, both `pyaml` and `pyyaml` exist, the former being mainly used for pretty-printing.
As we don't print anything, we can depend on `pyyaml` instead.

requirements.txt

@@ -3,5 +3,5 @@ ruff
 pytest
 
 # testing
-pyaml
+pyyaml
 pytest