[doc] fix sphinx warnings

5 jobs for master in 10 minutes and 34 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #226902
docker
build_linux_37

00:06:08

70.0%
passed #226903
docker
build_linux_38

00:06:06

70.0%
passed #226900
intel macos
build_macos_intel_37

00:09:39

70.0%
passed #226901
intel macos
build_macos_intel_38

00:09:43

70.0%
 
  Deploy
passed #226904
docker
deploy_beta

00:00:51