This implements a fake OIDC server, which intercepts calls to the HTTP client.
Improves accuracy of tests by covering more internal methods.

One particular example was the ID token validation, which previously mocked.

This uncovered an incorrect dependency: Synapse actually requires at least
authlib 0.15.1, not 0.14.0.

* Don't pin dev-deps in pyproject; use lower bounds

This makes it slightly less tedious to update these things via
successive dependabot updates, by reducing the likelihood of a merge
conflict.

* Changelog

* Changelog

* Fix `track_memory_usage` on poetry-core 1.3.x installations

The same kind of problem as discussed in #14085:

1. we defined an extra with an underscore
2. we look it up at runtime with an underscore
3. but poetry-core 1.3.x. installs it with a dash, causing (2) to fail.

Fix by using a dash everywhere.

* Changelog

Signed-off-by: Ivan Shapovalov <intelfx@intelfx.name>

* Revert to prior build-system requirements

This reverts #14080.

* Use normalised extra name, which poetry-core 1.3 will generate anyway

* Changelog

* Upper bound build-system requirements

* Remove upgrade note; expand changelog entry a little.

* Fix typo in build-system comment

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Pin build-system requirements

* Changelog

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: GitHub Actions <github-actions[bot]@users.noreply.github.com>

* Fix sdist to include rust build script

Fixes #13851

* Newsfile