Move upgrade downgrade tests to GitHub larger runners

[frouioui]

Description

This PR moves the upgrade/downgrade tests to GitHub Larger runners. The dedicated runner name is gh-runner-upgrade-downgrade-16cores-1 and has 16-cores. The machine can scale up to 100 times, supporting 100 concurrent workflows.

When comparing an upgrade downgrade test (Run Upgrade Downgrade Test - Query Serving (Schema)) ran on PR #13835 (https://github.com/vitessio/vitess/actions/runs/5956621188/job/16157782259?pr=13835) and the same workflow but ran with the larger runners (https://github.com/vitessio/vitess/actions/runs/5957296442/job/16159769723) we can see we saved about 50% of the time needed to run the workflow.

Related Issue(s)

Checklist

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

Deployment Notes

[vitess-bot]

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