Seems like in standalone.py, if config.MONGOD_EXECUTABLE is set through the command line, we prioritize using that version over the binary version assigned in ReplicaSetFixture. However, SERVER-44420 made changes such that the config options for MONGOD_EXECUTABLE will never be None. As a result, the binary version assigned in RepliaSetFixture will never be used, as we always give priority to config.MONGOD_EXECUTABLE.

Currently, as a result, all multiversion passthrough tests are actually running replica sets with 4.3 binaries, which is giving us false test coverage.