Use Oracle Linux 9 as base image

[jnoordsij]

This updates the base OS image to Oracle Linux 9, as a follow-up to #1046.

However, currently the innovation release only has a Docker-specific package for v8 (see https://repo.mysql.com/yum/mysql-innovation-community/docker/el/), where both 8.0 and 8.4 do have v9 specific releases. Given that the recent 8.0.37 is the only version in the 8.0 series with a v9 package (see https://repo.mysql.com/yum/mysql-8.0-community/docker/el/9/x86_64/), I suspect that going forward v9 packages will be released and the next innovation release will also have a v9 variant.

Therefore it's probably wise to:

• Merge this now and make sure to doublecheck this at the next innovation release, to remove the variant override added here;
• Hold off on merging this until the next innovation release (in approx. 3 months) and then update all images at once.

[tianon]

Very nice - I looked at this and was also grappling with "what do we do about innovation?" 😄

I think this is a good compromise and we can revisit when it gets a new release (since this will work, and give us the new release automatically so that we are likely to notice it, and then it's easy to update).