[Test] Fix test failure caused by invalid iOS version for availability

[rintaro]

20.0 is not a valid version number for iOS

Since it's translated to 27.0, the test failed with:

/Users/rintaro/Repositories/swift-oss/swift/test/SourceKit/DocSupport/doc_swift_module_availability_maccatalyst_is_deprecated.swift:15:16: error: CHECK-NEXT: expected string not found in input
// CHECK-NEXT: key.deprecated: "20.0"
               ^
<stdin>:87:57: note: scanning from here
 key.platform: source.availability.platform.maccatalyst,
                                                        ^
<stdin>:88:2: note: possible intended match here
 key.deprecated: "27.0"
 ^

rdar://155463166

[rintaro]

@swift-ci Please smoke test