Goldman Sachs gave the salad stock a thumbs-down.Shares of Sweetgreen (SG 0.16%) were heading lower again this week as a broader sell-off in growth stocks and a reaffirmed sell rating from Goldman Sachs weighed on the struggling fast-casual salad chain. Even an upbeat report from Starbucks wasn't enough to give Sweetgreen a boost, and the fast-casual stock was down 15.1% for the week as of 2:05 p.m. ET, according to data from S&P Global Market Intelligence. Sweetgreen slides againThere was no major news out ...