Release 13.21

[finnschiermer]

What, How & Why?

☑️ ToDos

• 📝 Changelog update
• 🚦 Tests (or not relevant)
• C-API, if public C++ API changed.

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: realm-ci.
This is most likely caused by a git client misconfiguration; please make sure to:

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