ci: fix vale by pinning the ubuntu image to 22.04

[codebyuma]

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Summary

Fixes DOC-1029 by pinning the ubuntu image to 22.04 for the Vale lint docs action. Similar to what we've done for the SDK and docs repos.

I'll keep the action disabled for now so that it doesn't impact other PRs but will re-enable it after this is merged and confirm that it works.

Background info:

• error: externally-managed-environment on ubuntu ubuntu-24.04 errata-ai/vale-action#128
• https://github.blog/changelog/2024-09-25-actions-new-images-and-ubuntu-latest-changes/

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