Correct two spelling mistakes in Differential

Summary: Closes T15269

Test Plan: Only changes to spelling.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15269

Differential Revision: https://we.phorge.it/D25252