Guacamole-manual CI (docker) build is broken

building [html]: targets for 33 source files that are out of date
updating environment: [new config] 33 added, 0 changed, 0 removed
reading sources... [  3%] adhoc-connections
reading sources... [  6%] administration
reading sources... [  9%] cas-auth
reading sources... [ 12%] configuring-guacamole

Exception occurred:
  File "/usr/local/lib/python3.10/site-packages/sphinx/ext/extlinks.py", line 103, in role
    title = caption % part
TypeError: not all arguments converted during string formatting
The full traceback has been saved in /tmp/sphinx-err-e3_b8cz7.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make: *** [Makefile:47: build/html/index.html] Error 2
Removing intermediate container 5191ca81541e
The command '/bin/sh -c make' returned a non-zero code: 2
Error: Process completed with exit code 2.