pbulk - limit build of python packages to one version only

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hello all,

I use pbulk to create my custom pkgsrc repository. Today I noticed that 
by default all Python packages in my limited_list seem to build variants 
of all supported Python versions.... 3.7, 3.8, 3.9, 3.10.

Since I usually don't need the older versions - what would be the 
recommended way to build either only the packages for a Python version I 
specify, or gladly only for the default Python version provided by pkgsrc?

Kind regards
Matthias