Merge tag 'v1.38.0rc2' into develop

Synapse 1.38.0rc2 (2021-07-09)
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Bugfixes
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- Fix bug where inbound federation in a room could be delayed due to not correctly dropping a lock. Introduced in v1.37.1. ([\#10336](https://github.com/matrix-org/synapse/issues/10336))

Improved Documentation
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- Update links to documentation in the sample config. Contributed by @dklimpel. ([\#10287](https://github.com/matrix-org/synapse/issues/10287))
- Fix broken links in [INSTALL.md](INSTALL.md). Contributed by @dklimpel. ([\#10331](https://github.com/matrix-org/synapse/issues/10331))