docs: Add release notes for 3.6.8

[devin-ai-integration]

Adds release notes for the Prefect 3.6.8 patch release.

Changes

Release Notes (version-3-6.mdx)

• Added 3.6.8 section with categorized changes:
  • 1 Enhancement (automation template URL property)
  • 1 Bug Fix (CDK/ECS warning)
  • 2 Development & Tidiness items (CI improvements, test fixes)
  • 1 Documentation update (MCP server security)

OpenAPI Schema (schema.json)

• Regenerated schema reflects removal of parameters and context fields from task run creation endpoint

Human Review Checklist

• Verify the OpenAPI schema changes are intentional (removal of parameters and context fields)
• Confirm all relevant PRs since 3.6.7 are included in the release notes
• Provide a release title/subtitle for 3.6.8 (e.g., "3.6.8 - [Title]")

---

Link to Devin run: https://app.devin.ai/sessions/ba3e69d0372b430fb82bb57127625217
Requested by: unknown ()

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

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