Merge branch 'develop' into matrix-org-hotfixes

Author: richvdh

CHANGES.md

@@ -0,0 +1 @@
+Check for unreachable code with mypy.

changelog.d/7124.bugfix

@@ -6,6 +6,7 @@ check_untyped_defs = True
 show_error_codes = True
 show_traceback = True
 mypy_path = stubs
+warn_unreachable = True
 files =
   synapse/api,
   synapse/appservice,

changelog.d/7796.bugfix

@@ -48,7 +48,7 @@
 except ImportError:
     pass
 
-__version__ = "1.20.1"
+__version__ = "1.21.0rc1"
 
 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