Ubuntu 22.04 doesn't meet our SQLite minimum version policy but we still build packages for it

From https://element-hq.github.io/synapse/latest/deprecation_policy.html#platform-dependencies:

> The oldest supported version of SQLite is the version [provided](https://packages.debian.org/oldstable/libsqlite3-0) by [Debian oldstable](https://wiki.debian.org/DebianOldStable).

This is currently 3.40.

Ubuntu 22.04 however provides [3.37.2](https://ubuntu.pkgs.org/22.04/ubuntu-main-arm64/libsqlite3-0_3.37.2-2_arm64.deb.html).

[SQLite 3.38.0 introduces the JSON operators](https://sqlite.org/json1.html#the_and_operators) `->` and `->>`, which I used in sticky events, so
this divergence is actually somewhat meaningful.

Possible outcomes here:

- redefine our support policy for Ubuntu releases (well, maybe we should do this anyway)
- stop building for Ub22.04 (and finding some way to upgrade olddeps CI)

Start with the deprecation policy section linked in the issue, then inspect the Ubuntu 22.04 package-building setup and olddeps CI mentioned in the proposed outcomes. The work is done when one support-policy or build-support decision is agreed and reflected consistently in the relevant configuration and documentation.

Written by the indexing model from the issue text.