Merge tag 'v1.51.0rc2' into develop

Synapse 1.51.0rc2 (2022-01-24)
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Bugfixes
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- Fix a bug introduced in Synapse 1.40.0 that caused Synapse to fail to process incoming federation traffic after handling a large amount of events in a v1 room. ([\#11806](https://github.com/matrix-org/synapse/issues/11806))