fix indentation of reference

Author: jwarner8

src/CSET/recipes/verification/surface_categorical_model_obs_fb.yaml

@@ -43,8 +43,9 @@ description: |
     necessarily imply a skillful forecast, as hits and false alarms may compensate
     for one another.
 
-References
-https://scores.readthedocs.io/en/stable/api.html#scores.categorical.BasicContingencyManager.frequency_bias
+    References
+    https://scores.readthedocs.io/en/stable/api.html#scores.categorical.BasicContingencyManager.frequency_bias
+
 steps:
   - operator: read.read_cubes
     file_paths: $INPUT_PATHS