Fix Version/s: None
As per jenkins job :
the lsstsw rebuild is failing on the following test:
After some investigation, it is found that the lsst-build prepare is checking out master for the package
that has been changed since the weekly 23 has been done, on which 18.0.0 is based.
Further checks show also that other DM External packages are checkout with the master version.
The package autograd, for example, is also cloned, despite it was not part of the weekly 23.
It seems that lsst_build need some extra logic to properly clone and checkout the DM External packages.