Run ScyllaDB in production mode in CI

[jvff]

Motivation

PR #2702 made ScyllaDB run in production mode in the Docker compose configuration, but that had to be disabled in order to run in CI. That's because GitHub's runners don't support configuring a necessary kernel parameter.

Proposal

Run the Docker CI workflow in a custom runner, and make ScyllaDB run in production mode again, by removing the patch in the CI job.