Adapting Checking-in Changes to Our Project to new versions of venv

[fiveop]

Newer version of venv create a .gitignore file in the environment directory, if invoked via CLI (see python/cpython#108125). Therefore the directory will not show up in git status after creation and changes to the root .gitignore are not necessary.

The section “Checking-in Changes to Our Project” needs to be adapted to that change.