This is to help with performance, where trying to connect to thousands
of hosts at once can consume a lot of CPU (due to TLS etc).

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

By referring to awaitables instead of deferreds.

This is part of fixing #6116: we want to put RC debs into a different place than release debs, so reprepro has to be able to tell them apart.

A few things here:

* Build the debs for single distro for each PR, so that we can see if it breaks. Do the same for develop. Building all the debs ties up the GHA workers for ages.
* Stop building the debs for release branches. Again, it takes ages, and I don't think anyone is actually going to stop and look at them. We'll know they are working when we make an RC.
* Change the configs so that if we manually cancel a workflow, it actually does something.

Fix messages from multiple senders in historical chunk. This also means that an app service does not need to define `?user_id` when using this endpoint.

Follow-up to https://github.com/matrix-org/synapse/pull/9247

Part of MSC2716: https://github.com/matrix-org/matrix-doc/pull/2716

Previously only world-readable rooms were shown. This means that
rooms which are public, knockable, or invite-only with a pending invitation,
are included in a space summary. It also applies the same logic to
the experimental room version from MSC3083 -- if a user has access
to the proper allowed rooms then it is shown in the spaces summary.

This change is made per MSC3173 allowing stripped state of a room to
be shown to any potential room joiner.

Fixes: #10338

This PR is tantamount to running:

    python3.8 -m com2ann -v 6 tests/

(com2ann requires python 3.8 to run)

We should be reporting the age rather than absolute timestamp.

GHA workflow to build the debs

while I'm dealing with INTEGERs and BIGINTs, let's replace room_depth.min_depth
with a BIGINT.

... now that it has been fixed in https://github.com/matrix-org/sytest/pull/1061.

This reverts commit 944428d1.

Fix the user directory becoming broken (and noisy errors being logged) when knocking and room statistics are in use. (#10344)

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

Synapse 1.38.0rc2 (2021-07-09)
==============================

Bugfixes
--------

- 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
----------------------

- 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))