fix: wrong path on migrated venv

[sk1234567891]

Thanks for contributing, make sure you address all the checklists (for details on how see development documentation)

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

[pfmoore]

Is there an issue for this? It's hard to see how __VIRTUAL_ENV__ could be incorrect here so an issue with a demonstration of how to reproduce the problem would be helpful.

Also, this would presumably need to be fixed the same way in all the activate scripts, not just the bash one?