Fix typo "recipeint" in metamta.one-mail-per-recipient description
Test Plan: Go to `/config/settings/all` and look at the description of `metamta.one-mail-per-recipient`
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25311