[ci] Split up large rsc-build-errors development test (#95624)
See https://github.com/vercel/next.js/pull/95553 for an explanation of
why we want to split these up. TL;DR it makes CI faster and saves us
some money.
In CI we have to run tests at the suite/file granularity, so if a test
suite is too long it limits parallelism and if it has to be retried, we
have to retry the full suite.
