This PR updates the build tags that we perform Complement runs with to match our [buildkite pipeline](618b3e90bc/synapse/pipeline.yml (L570)), as well as adding `msc2403` (as it will be required once #9359 is merged). Build tags are what we use to determine which tests to run in Complement (really it determines which test files are compiled into the final binary).
I haven't put in a comment about updating the buildkite side here, as we've decided to migrate fully to GitHub Actions anyhow.
Andrew Morgan