sphinx apparently does not play well with multiple build targets in a single command: change the "docs" build comamnd to run the html build and the link check in separate commands

Author: mattsb42-aws

tox.ini

@@ -259,7 +259,8 @@ commands =
 basepython = python3
 deps = -rdoc/requirements.txt
 commands =
-    sphinx-build -E -c doc/ -b html -b linkcheck doc/ doc/build/html
+    sphinx-build -E -c doc/ -b html doc/ doc/build/html
+    sphinx-build -E -c doc/ -b linkcheck doc/ doc/build/html
 
 [testenv:serve-docs]
 basepython = python3