roachtest: update mixedversion's logic for performing skip-version upgrades

At the time the logic for skip-version upgrades was added, we were working with the assumption that version skipping would be a feature supported starting from some version. That's reflected by the current implementation's definition of a `minSupportedSkipVersionUpgrade` [1] variable.

However, we now know a release can be skipped if it's an _innovation_ release. We need to fix the logic in the `mixedversion` framework to implement that logic.

Ideally, we would be able to consume structured data from some source telling us whether a release has the "innovation" status. We already consume release data from the `releases.yaml` file maintained by the docs team. Maybe we can do something similar here. See [preliminary internal discussion](https://cockroachlabs.slack.com/archives/C4A9ALLRL/p1723148757838219) on this topic.

[1] https://github.com/cockroachdb/cockroach/blob/fe49f7cb5d9b2d74a3d02765891d1f0e814ffd8b/pkg/cmd/roachtest/roachtestutil/mixedversion/mixedversion.go#L486

Jira issue: CRDB-41361