fix/venv activation

[carpawell]

I have been looking at errors like

patch -R --dry-run -p1 -s -f -d venv.local-pytest/bin/ < build_assets/activate.patch || patch -p1 -d venv.local-pytest/bin/ < build_assets/activate.patch
2 out of 2 hunks FAILED

and

make: *** No rule to make target 'env'.  Stop.
deactivate:unset:28: not enough arguments
(venv.local-pytest)

for years already. Double check, please. The whole approach looks strange to me but fixing smth is never bad.