Update admin deletion setting migration

What does this MR do and why?

Follow-up from !86568 (merged).

It's fine to use a transaction here since we're only executing a single update on a single row. Skipping the transaction would also be safe, but I prefer to make migrations as simple as they can possibly be in case someone needs to read one quickly.

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MR acceptance checklist

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Related to #365129 (closed)