Package check()ing was failing with an error about not finding dependencies that were actually correctly installed in the previous steps in the library at the environment variable R_LIBS_USER.
The problem was that the library at R_LIBS_USER appeared last in .libPaths() just after .Library and .Library.site. The order in .libPaths() is determined at startup from the environment variables R_LIBS and R_LIBS_USER, in that order.
By default, R_LIBS is unset, causing R_LIBS_USER to appear first in .libPaths().
However, the docker images rocker/verse set R_LIBS within $R_HOME/etc/Renviron.site.
The current solution prevents reading this file at start up using --no-environ, only for check().