Fix codegen command with the right type

[dbussink]

This was broken with the new pool.

Related Issue(s)

Broken in #14034

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

[vitess-bot]

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