Make the environment_variables test less flaky.
Make the environment_variables test less flaky.

The test was inadvertently depending on the ordering of output between
stderr and stdout, which makes it break particularly when being run
remotely.

rdar://88335113

JGiola/swift,apple/swift,apple/swift,rudkx/swift,ahoppen/swift,gregomni/swift,apple/swift,JGiola/swift,atrick/swift,benlangmuir/swift,benlangmuir/swift,gregomni/swift,rudkx/swift,gregomni/swift,rudkx/swift,ahoppen/swift,apple/swift,glessard/swift,roambotics/swift,ahoppen/swift,apple/swift,roambotics/swift,rudkx/swift,glessard/swift,gregomni/swift,apple/swift,roambotics/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,ahoppen/swift,glessard/swift,atrick/swift,gregomni/swift,JGiola/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift,atrick/swift,roambotics/swift,ahoppen/swift,benlangmuir/swift,roambotics/swift,glessard/swift,glessard/swift,atrick/swift,rudkx/swift,glessard/swift,JGiola/swift,JGiola/swift,benlangmuir/swift,rudkx/swift,atrick/swift,atrick/swift