By Stephanie Kelly NEW YORK (Reuters) -Oil prices sank around 3% on Thursday as OPEC+ confirmed it would only increase output in August as much as previously announced despite tight global supplies, but left the market wondering about future output. Brent crude futures for September delivery fell $3.42, or 3%, to settle at $109.03 per barrel. The August contract, which expires on Thursday, fell $1.45, or 1.3%, to settle at $114.81 a barrel. U.S. West Texas Intermediate (WTI) crude futures fell $4.02, or 3.7%, to settle at $105.76 a barrel. The OPEC+ group of producers, including Russia, on Thu…