MSC4140: don't cancel delayed state on own state

[AndrewFerr]

When a user sends a state event, do not cancel their own delayed events for the same piece of state.

For context, see the relevant section in the MSC.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct
  (run the linters)

[AndrewFerr]

Depends on matrix-org/complement#742 for Complement tests to pass.

[anoadragon453]

Looks good on the whole, just some small points of feedback.

[AndrewFerr]

The sytests pass when I run them locally. Is there a way to retry their CI runs?

[MadLittleMods]

@AndrewFerr Retried 👍

[AndrewFerr]

Now the only failing tests are the ones that depend on matrix-org/complement#742 (finally!).

[hughns]

@AndrewFerr what's the latest on this PR and addressing any outstanding issues?

[AndrewFerr]

what's the latest on this PR and addressing any outstanding issues?

This and matrix-org/complement#742 are both ready to be merged (though the latter should be merged first).

EDIT: I'll open a new Complement PR with its branch name set such that it will be used in this PR's Complement tests in CI.

[AndrewFerr]

Eugh, looks like I had the wrong understanding of how CI chooses which Complement branch to run on.

In any case, I can assure you that TestDelayedEvents passes when using this PR + matrix-org/complement#768.

[anoadragon453]

This LGTM, thanks for your patience 🙏

Will merge this PR at the same time as matrix-org/complement#768.