Fixed building documentation

Author: coot

doc/requirements.txt

@@ -37,7 +37,7 @@ pygments==2.14.0
     #   sphinx
 pytz==2021.3
     # via babel
-pyyaml==5.4.1
+pyyaml==6.0.1
     # via sphinx-jsonschema
 requests==2.26.0
     # via