CI: Upgrade/Downgrade use N+1 version of vtctld when testing with N+1 of vttablet

[rohit-nayak-ps]

Description

Makes a similar change done in the multi-tenant PR at https://github.com/vitessio/vitess/pull/15503/files#diff-79c61525895b1e17d0cc49054a0d19f9264073042bbe75a8f5997092f02a3c92R203-R210

We need to use the same version of vtctld as vttablets.

Otherwise this workflow fails since it cannot insert into _vt.vreplication which now has a json column for which we cannot specify a default at the table schema level.

This is being done directly on v19 since the versions of vttablet/vtctlds of upgrade/downgrade are reversed as compared to main (v20) and v19.

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[deepthi]

In general we want all combinations of versions to work. So why is this PR acceptable?

• The specific tests are meant to test vttablet/vtgate cross-version compatibility. vtctld is somewhat incidental to the testing
• the reference test creates a Materialize workflow while the cluster is in mixed-version mode. This is not something that we support in production. You create your workflow on a stable cluster, and it will continue working through upgrades/downgrades.
• the current upgrade/downgrade testing framework does not make it easy to start a test, and then do an upgrade/downgrade. It first does the upgrade/downgrade and then runs a bunch of existing e2e tests.