[CI] Testing legacy client with the new runtime

[Dinonard]

Description

After the v5.42.0 release, an issue was detected where an old client couldn't run the new runtime.
This is perfectly normal when a new runtime requires updated host functions, as was the case with this particular release.

However, such changes should be detected via CI.
As part of this task, we should implement such a check in the release process.

1. Find the latest existing release which contains the client & fetch it
2. Start it up using the zombienet tool
3. Verify runtime upgrade using the new runtime wasm blob
4. Ensure upgrade happens & block production continues

[Dinonard]

Perhaps best to do after: #1347