[test] Move availability tests to later fake OS versions
10.50 was once greater than any real macOS version, but now it compares
less than real released versions, which makes these tests depend on the
deployment target unnecessarily. Update these tests to use even larger
numbers to hopefully keep them independent a little longer.
(cherry picked from commit fd1875dcfbb752a770c64a478b27a79b8b01267e)
Conflicts:
test/Interpreter/Inputs/availability_zippered.swift
test/Parse/availability_query_unavailability.swift
test/decl/enum/derived_hashable_equatable_macos.swift
(cherry picked from commit 3e76bb53896ac6df15d991dc5fc9e9f2fa5ec8b0)
