When building documentation using sphinx we see ~1200 similar warnings [0]
[0] - https://s3-logs.fd.io/vex-yul-rot-jenkins-1/csit-verify-tox-master-ubuntu2004-x86_64/3289/doc_verify.log.gz
These warning are harmless and can be fixed later
Signed-off-by: Viliam Luc <vluc@cisco.com>
Change-Id: I1ac1099d38935971d47491dde905715345d3935c