Print the black version used

[nrnhines]

When local black formatting differs from the CI, it is helpful to know what black, python, and virtual environment was used.

For the "Check formatting / C/C++, CMake and Python (pull_request)" CI
the log, in the "Check formatting" section will show something like

=== Black version used by coding-conventions/format ===
black: 22.12.0
Python: 3.10.12
Interpreter: /home/runner/work/nrn/nrn/.bbp-project-venv/bin/python

See neuronsimulator/nrn#3782