CAMEL-24548 CAMEL-24549: Sync backport upgrade guides

[oscerd]

Adds the 4.18.5 and 4.22.1 symlink-aware download-containment notes to the canonical versioned upgrade guides on main. The text mirrors the documentation shipped by backport PRs #25991 and #25990.

This is a documentation-only follow-up to #25873; no runtime code changes are included.

Generated by Codex via OSS Helper on behalf of oscerd

Co-authored-by: Codex noreply@openai.com

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