Merge tag 'v1.39.0rc3' into develop

Synapse 1.39.0rc3 (2021-07-28)
==============================

Bugfixes
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- Fix a bug introduced in Synapse 1.38 which caused an exception at startup when SAML authentication was enabled. ([\#10477](https://github.com/matrix-org/synapse/issues/10477))
- Fix a long-standing bug where Synapse would not inform clients that a device had exhausted its one-time-key pool, potentially causing problems decrypting events. ([\#10485](https://github.com/matrix-org/synapse/issues/10485))
- Fix reporting old R30 stats as R30v2 stats. Introduced in v1.39.0rc1. ([\#10486](https://github.com/matrix-org/synapse/issues/10486))

Internal Changes
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- Fix an error which prevented the Github Actions workflow to build the docker images from running. ([\#10461](https://github.com/matrix-org/synapse/issues/10461))
- Fix release script to correctly version debian changelog when doing RCs. ([\#10465](https://github.com/matrix-org/synapse/issues/10465))