chore: Update release notes sop

[zastrowm]

Description

Update the release notes SOP that was most effective after several iterations of having it generate the v1.21.0 release notes - final flow is at zastrowm#19.

The flow on this was tweaking the SOP and then running the agent, and attempting to have it update in response. The biggest problems to solve was that:

• It blindly trusted examples in PRs, resulting in examples that were wrong because of stale PRs
• It would not generate useful tests

I do not have the step-by-steps results with the different prompt variants as I deleted the older issues to avoid too many references being added to old PRs, but viewing the final issue with results shows the SOP results with one shot run after verifying which features should go in.

Type of Change

Agent Change

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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