[16.0] Fix: TabletServer ReserveBeginExecute to return transaction ID on error

[harshit-gangal]

Description

This PR fixes the issue with ReserveBeginExecute to return transaction ID on error.
Without this fix, the transaction was lost and was only cleared by the transaction killer.

There is a separate PR for main: #13127

Related Issue(s)

• Fixes Bug Report: ReserveBeginExecute missing returning transaction ID on error #13192

Checklist

• "Backport to:" labels have been added if this change should be back-ported 15.0
• 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

Deployment Notes

[vitess-bot]

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