[pdelsante]

Goal

Stop restoring a virtualenv that was built with a different Python patch release.

Why

The venv cache key is <ref>-venv-<requirements hash>. A venv links to its interpreter by full path (/opt/hostedtoolcache/Python/3.14.9/...). On certego/babel#33 the runner moved from 3.14.9 to 3.14.8, the cached venv was restored anyway, and Run linters failed with .venv/bin/black: cannot execute: required file not found. Rerunning the job does not help.

How

1. restore_virtualenv and save_virtualenv read the runner's Python version (platform.python_version()) in a new step.
2. The key becomes <ref>-venv-py<X.Y.Z>-<requirements hash>. Inputs and callers are unchanged.
3. Updated both action READMEs, and the hardlinked copies under .github/.

Out of scope

• The pip cache key is left as it is: wheels are not tied to the interpreter path.
• Entries saved under the old key format just stop matching and expire, so there is no migration.

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