Merge tag 'v1.21.0rc3' into develop

Synapse 1.21.0rc3 (2020-10-08)
==============================

Bugfixes
--------

- Fix duplication of events on high traffic servers, caused by PostgreSQL `could not serialize access due to concurrent update` errors. ([\#8456](#8456))

Internal Changes
----------------

- Add Groovy Gorilla to the list of distributions we build `.deb`s for. ([\#8475](#8475))

Author: erikjohnston

CHANGES.md

@@ -1,3 +1,18 @@
+Synapse 1.21.0rc3 (2020-10-08)
+==============================
+
+Bugfixes
+--------
+
+- Fix duplication of events on high traffic servers, caused by PostgreSQL `could not serialize access due to concurrent update` errors. ([\#8456](https://github.com/matrix-org/synapse/issues/8456))
+
+
+Internal Changes
+----------------
+
+- Add Groovy Gorilla to the list of distributions we build `.deb`s for. ([\#8475](https://github.com/matrix-org/synapse/issues/8475))
+
+
 Synapse 1.21.0rc2 (2020-10-02)
 ==============================
 

changelog.d/8456.misc

@@ -48,7 +48,7 @@
 except ImportError:
     pass
 
-__version__ = "1.21.0rc2"
+__version__ = "1.21.0rc3"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when