[ci] Failure Bot: run only on PR merge, allowed auto-retry

Run the workflow only when pull requests are merged.
Enabled auto-retry by adding write permissions to the action workflow.

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Co-authored-by: Sarthak Tyagi <142912014+stktyagi@users.noreply.github.com>
Co-authored-by: stktyagi <stktyagi2810@gmail.com>

Author: nemesifier