Align validation runtime version policy across CI and reusable workflows

[hdamker]

Problem description

The validation workflow runtime versions should be explicit and aligned across the reusable validation workflow and the PR-time Tooling CI checks that validate it.

The Node.js side has been handled in #341: Tooling CI's validation-facing jobs are aligned with the reusable validation workflow's Node 24 runtime. The remaining open point is Python. The validation workflow and Tooling CI currently pin Python 3.11, and related validation/release workflows and shared actions also pin Python 3.11. The intended Python runtime policy should be reviewed and made explicit so PR-time checks, reusable workflows, and local validation setup do not drift.

Expected action

• Treat ci(validation): align tooling CI with Node 24 #341 as the Node runtime alignment fix.
• Decide the Python runtime policy for validation and adjacent tooling workflows: keep Python 3.11, move to Python 3.12, or define a supported range.
• Update Python runtime usage in a separate PR after that decision.
• Make Tooling CI and the reusable validation workflow use the same chosen Python runtime.
• Document local validation setup expectations if local development may use a different Python version than CI.

Additional context

This was identified while working on validation dependency and CI consistency. Keeping Python alignment as a separate issue avoids mixing runtime-policy changes with dependency replacement or Node-runtime alignment.