ICU is an optional dependency and also a pain to install. Mention that
you can just not install it and still get a working installation.

Some links seemed to be incorrect (vector-im/sygnal and vector-im/sytest
have never been A Thing iirc) so pointed them back to matrix-org/*).

Introduced in #16833

Fixes #16844

Downgrade the `download-artifact` and `upload-artifact` actions to v3 due to breaking changes. (#16847)

Partially reverts #16796

This is causing errors of the form:

```
Error: Failed to CreateArtifact: Received non-retryable error: Failed request: (409) Conflict: an artifact with this name already exists on the workflow run
```

for the debs and wheels stages.


There were breaking changes that weren't included in the dependabot
changelog (:/):
https://github.com/actions/upload-artifact#breaking-changes




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Original commit schedule, with full messages:

<ol>
<li>

Downgrade the `upload-artifact` and `download-artifact` actions to v3 

</li>
</ol>

---------

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

This helps with bot accounts with lots of non-e2e devices.

The change is basically to change the order of the join for the case of
using `INNER JOIN`

During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.

Pulled out of #16803 since the drive-by cleanup was maybe not as
drive-by as I had hoped.

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Original commit schedule, with full messages:

<ol>
<li>

Add a --generate-only option 

</li>
</ol>

---------

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

More info [here](https://www.nginx.com/blog/nginx-plus-r30-released/).

Nginx threw error's at me when I used all the options of the doc

Allow room creation but not publishing to continue if room publication rules are violated when creating a new room. (#16811)

Prior to this PR, if a request to create a public (public as in
published to the rooms directory) room violated the room list
publication rules set in the
[config](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#room_list_publication_rules),
the request to create the room was denied and the room was not created.

This PR changes the behavior such that when a request to create a room
published to the directory violates room list publication rules, the
room is still created but the room is not published to the directory.

The ecosystem e.g. regex crate, have bumped up their MSRV to 1.65.0,
which was released Nov 2022. In line with our policy, let's bump to
match.