Mark another thorough String test as requiring an optimized stdlib (#21835)
Mark another thorough String test as requiring an optimized stdlib (#21835)

This one's taking a pretty long time on simulators, only sometimes
making it under the timeout limit.
amraboelela/swift,shahmishal/swift,benlangmuir/swift,rudkx/swift,sschiau/swift,lorentey/swift,xedin/swift,benlangmuir/swift,atrick/swift,jmgc/swift,airspeedswift/swift,harlanhaskins/swift,shahmishal/swift,karwa/swift,allevato/swift,shahmishal/swift,glessard/swift,lorentey/swift,CodaFi/swift,roambotics/swift,apple/swift,stephentyrone/swift,ahoppen/swift,nathawes/swift,practicalswift/swift,CodaFi/swift,devincoughlin/swift,jmgc/swift,gribozavr/swift,lorentey/swift,airspeedswift/swift,amraboelela/swift,airspeedswift/swift,devincoughlin/swift,xedin/swift,JGiola/swift,practicalswift/swift,parkera/swift,xwu/swift,parkera/swift,practicalswift/swift,practicalswift/swift,stephentyrone/swift,sschiau/swift,atrick/swift,CodaFi/swift,apple/swift,aschwaighofer/swift,karwa/swift,practicalswift/swift,rudkx/swift,rudkx/swift,roambotics/swift,shajrawi/swift,airspeedswift/swift,stephentyrone/swift,CodaFi/swift,shajrawi/swift,glessard/swift,sschiau/swift,aschwaighofer/swift,jckarter/swift,xwu/swift,atrick/swift,allevato/swift,shajrawi/swift,jckarter/swift,jckarter/swift,apple/swift,tkremenek/swift,apple/swift,stephentyrone/swift,airspeedswift/swift,nathawes/swift,parkera/swift,sschiau/swift,sschiau/swift,ahoppen/swift,jckarter/swift,ahoppen/swift,xedin/swift,parkera/swift,nathawes/swift,CodaFi/swift,devincoughlin/swift,jmgc/swift,xwu/swift,xwu/swift,harlanhaskins/swift,jckarter/swift,devincoughlin/swift,gribozavr/swift,aschwaighofer/swift,tkremenek/swift,gregomni/swift,gregomni/swift,xwu/swift,apple/swift,shajrawi/swift,gribozavr/swift,hooman/swift,parkera/swift,karwa/swift,aschwaighofer/swift,devincoughlin/swift,harlanhaskins/swift,atrick/swift,shajrawi/swift,gregomni/swift,ahoppen/swift,devincoughlin/swift,hooman/swift,practicalswift/swift,benlangmuir/swift,JGiola/swift,shahmishal/swift,glessard/swift,amraboelela/swift,aschwaighofer/swift,benlangmuir/swift,ahoppen/swift,rudkx/swift,nathawes/swift,xedin/swift,harlanhaskins/swift,shahmishal/swift,glessard/swift,gribozavr/swift,jmgc/swift,glessard/swift,parkera/swift,sschiau/swift,hooman/swift,hooman/swift,xedin/swift,roambotics/swift,nathawes/swift,shahmishal/swift,JGiola/swift,gregomni/swift,devincoughlin/swift,tkremenek/swift,hooman/swift,lorentey/swift,rudkx/swift,allevato/swift,karwa/swift,nathawes/swift,practicalswift/swift,JGiola/swift,shahmishal/swift,amraboelela/swift,gribozavr/swift,allevato/swift,karwa/swift,benlangmuir/swift,gregomni/swift,allevato/swift,xedin/swift,gribozavr/swift,devincoughlin/swift,harlanhaskins/swift,karwa/swift,karwa/swift,jckarter/swift,tkremenek/swift,allevato/swift,airspeedswift/swift,JGiola/swift,aschwaighofer/swift,rudkx/swift,JGiola/swift,roambotics/swift,tkremenek/swift,hooman/swift,CodaFi/swift,stephentyrone/swift,ahoppen/swift,stephentyrone/swift,roambotics/swift,shahmishal/swift,hooman/swift,parkera/swift,apple/swift,harlanhaskins/swift,xedin/swift,allevato/swift,atrick/swift,jmgc/swift,stephentyrone/swift,airspeedswift/swift,sschiau/swift,xwu/swift,parkera/swift,jmgc/swift,gribozavr/swift,lorentey/swift,amraboelela/swift,roambotics/swift,lorentey/swift,jmgc/swift,benlangmuir/swift,gregomni/swift,tkremenek/swift,practicalswift/swift,harlanhaskins/swift,amraboelela/swift,gribozavr/swift,glessard/swift,sschiau/swift,xwu/swift,amraboelela/swift,lorentey/swift,CodaFi/swift,tkremenek/swift,shajrawi/swift,atrick/swift,nathawes/swift,lorentey/swift,aschwaighofer/swift,karwa/swift,shajrawi/swift,xedin/swift,shajrawi/swift,jckarter/swift