CI upgrade tests: separate paths for upgrade v8.0.0 and v9.0.0

[shlomi-noach]

Description

Yesterday we released https://github.com/vitessio/vitess/releases/tag/v9.0.0. From now on, we want to have CI verify that our PRs have valid upgrade path from v9.0.0.

I'm still keeping upgrade tests for v8.0.0 although I think we may not need to run them anymore? Any code we contribute from now on goes to > v9.0.0 version, and therefore should not necessarily be compatible with v8.0.0? cc @deepthi

So now there's two distinct CI tests, one called upgrade8 and one called upgrade9.

Checklist

• Should this PR be backported?
• Tests were added or are not required
• Documentation was added or is not required

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build/CI
• VTAdmin

[deepthi]

I'm still keeping upgrade tests for v8.0.0 although I think we may not need to run them anymore? Any code we contribute from now on goes to > v9.0.0 version, and therefore should not necessarily be compatible with v8.0.0?

That is correct.
We should plan to backport new migration tests to 9.0 and have them run against v8.0.0.

[shlomi-noach]

replaced by #7848