Use IS_BIOC_BUILD_MACHINE rather than BBS_HOME in skip_on_bioc() #1712
Description
https://bioconductor.org/checkResults/3.16/bioc-LATEST/Renviron.bioc (and the current 'devel' builds) defines IS_BIOC_BUILD_MACHINE=true to replace use of the ad hoc and undocumented BBS_HOME.