CI: Test OpenTitan integration #886
Description
With zerorisc/expo#184 merged, we should make sure that we don't break the integration with future changes.
https://github.com/pq-code-package/mlkem-native/blob/main/.github/workflows/integration-opentitan.yml can be an inspiration, but it has to be adapted as we cannot afford to run verilator-based tests in CI (they run 1.5 hours on my laptop). We can try only testing one parameter set. If that is still to slow, we may only be able to check that it compiles.