[Runtime] Fix const cast warning in ReflectionMirror.cpp
[Runtime] Fix const cast warning in ReflectionMirror.cpp

rdar://problem/70444932

xwu/swift,roambotics/swift,roambotics/swift,roambotics/swift,atrick/swift,xwu/swift,parkera/swift,apple/swift,parkera/swift,jmgc/swift,apple/swift,benlangmuir/swift,tkremenek/swift,apple/swift,ahoppen/swift,atrick/swift,xwu/swift,hooman/swift,atrick/swift,gregomni/swift,JGiola/swift,hooman/swift,jmgc/swift,tkremenek/swift,JGiola/swift,benlangmuir/swift,apple/swift,atrick/swift,tkremenek/swift,xwu/swift,glessard/swift,rudkx/swift,atrick/swift,parkera/swift,gregomni/swift,rudkx/swift,ahoppen/swift,hooman/swift,JGiola/swift,hooman/swift,atrick/swift,glessard/swift,jmgc/swift,benlangmuir/swift,jmgc/swift,benlangmuir/swift,benlangmuir/swift,apple/swift,ahoppen/swift,roambotics/swift,jmgc/swift,parkera/swift,rudkx/swift,gregomni/swift,xwu/swift,glessard/swift,ahoppen/swift,gregomni/swift,parkera/swift,JGiola/swift,rudkx/swift,hooman/swift,jmgc/swift,gregomni/swift,parkera/swift,jmgc/swift,hooman/swift,glessard/swift,parkera/swift,benlangmuir/swift,parkera/swift,xwu/swift,tkremenek/swift,glessard/swift,xwu/swift,tkremenek/swift,roambotics/swift,tkremenek/swift,ahoppen/swift,roambotics/swift,JGiola/swift,hooman/swift,tkremenek/swift,rudkx/swift,apple/swift,JGiola/swift,rudkx/swift,glessard/swift,ahoppen/swift,gregomni/swift