What happened?

Canary builds broke with the plugin PR #11960 when we added the pluggy dependency.

This is a revival of the same issue we encountered when we attempted to deprecated the vendored toolz.

Xref conda/conda-build#4561 conda/conda-build#4572 conda/conda-build#4604

Tasks

• Fix root cause: Run Python in isolated mode unless in dev mode conda-build#4604
• Test conda-build canary version to ensure the issue is resolved
• Release conda-build
• Set env var triggering the isolated build mode added in conda-build 3.23.0 #12115