Merge branch 'release-v1.13.0' of github.com:matrix-org/synapse into dinsic-release-v1.14.x

* 'release-v1.13.0' of github.com:matrix-org/synapse: (257 commits)
  Update changelog based on feedback.
  Move warnings in the changelog and re-iterate changes to branches.
  1.13.0
  update dh-virtualenv (#7526)
  1.13.0rc3
  Hash passwords earlier in the registration process (#7523)
  1.13.0rc2
  1.13.0rc2
  Stop `get_joined_users` corruption from custom statuses (#7376)
  Do not validate that the client dict is stable during UI Auth. (#7483)
  Fix new flake8 errors (#7489)
  Don't UPGRADE database rows
  RST indenting
  Put rollback instructions in upgrade notes
  Fix changelog typo
  Oh yeah, RST
  Absolute URL it is then
  Fix upgrade notes link
  Provide summary of upgrade issues in changelog. Fix )
  Move next version notes from changelog to upgrade notes
  ...

scripts-dev/build_debian_packages

@@ -27,6 +27,7 @@ DISTS = (
     "ubuntu:cosmic",
     "ubuntu:disco",
     "ubuntu:eoan",
+    "ubuntu:focal",
 )
 
 DESC = '''\