SFCGAL_CHECK_VALIDITY being ignored

According to https://oslandia.gitlab.io/SFCGAL/documentation.html it is possible to disable validity checks globally by setting SFCGAL_CHECK_VALIDITY=OFF.

When I do the cmake build like this cmake -DSFCGAL_CHECK_VALIDITY=OFF .. I get following warning:

#8 6.910 CMake Warning:
#8 6.910   Manually-specified variables were not used by the project:
#8 6.910
#8 6.910     SFCGAL_CHECK_VALIDITY
#8 6.910
#8 6.910

I'm using this Dockerfile for the build: https://github.com/postgis/docker-postgis/blob/master/13-master/Dockerfile The only modification I made is adding the cmake option as shown above.

Am I doing something wrong or is the cmake option no longer supported? If yes, which versions do support it?