[test] Update IRGen/metadata.swift to pass on later tvOS
This test has been failing on arm64-tvos-simulator forever, and after we
bumped the default deployment target is also failing on x86_64. Update
the test to match ios/watchos, which were already fixed in the past.
rdar://135453916
(cherry picked from commit 3b1571ee67929d4021029651c64afab27e2dbb22)
(cherry picked from commit 46fe4148443257adbbefbe9edcb3c091cf854be0)
