Manually downgrade yamlfix dependency

The `maison` dependency just had a new 2.0 release with breaking changes
(https://github.com/dbatten5/maison/releases/tag/v2.0.0) which break
yamlfix (see lyz-code/yamlfix#286).

.pre-commit-config.yaml

@@ -28,6 +28,8 @@ repos:
     hooks:
       - id: yamlfix
         exclude: packaging/conda/meta.yaml
+        language: python
+        additional_dependencies: [maison<2.0.0]
   - repo: https://github.com/python-jsonschema/check-jsonschema
     rev: 0.29.0
     hooks: