[Bug]: dbt-build is a no-op if only Python repos are in the work area

[jcfreeman2]

Description

Or, more precisely: if there are no packages in ./sourcecode, despite the presence of Python packages in ./pythoncode which we'd like installed we continue to get the traditional result when dbt-build is run:

No package repos have been found in /home/nfs/jcfree/NFD_DEV_260226_A9/sourcecode, 
so no C++ build will take place. However, a script saving the environment will
be put in /home/nfs/jcfree/NFD_DEV_260226_A9/install

...and dbt-build exits out. However, with the addition of Python package processing to dbt-build, if there are Python packages in ./pythoncode it should install them, regardless of whether there are no C++ packages in ./sourcecode.

Steps to reproduce

Create a work area, add a Python package to ./pythoncode, and run dbt-build. The Python package won't install.

Version and environment

daq-buildtools v8.13.0 with last night's nightly.

Impact

Small/Isolated

Anything else?

No response