Add ruamel.yaml for tests again

Author: tulir

setup.py

@@ -3,7 +3,7 @@
 from mautrix import __version__
 
 encryption_dependencies = ["python-olm", "unpaddedbase64", "pycryptodome"]
-test_dependencies = ["aiosqlite", "asyncpg", *encryption_dependencies]
+test_dependencies = ["aiosqlite", "asyncpg", "ruamel.yaml", *encryption_dependencies]
 
 setuptools.setup(
     name="mautrix",