Fixes BIOSError compilation error when compiling with Xcode 13

Xcode 12 and older incorrectly let us declare BIOSError.incorrectSize as @available(iOS 13), but Swift doesn't support @available for enum cases with associated values. Xcode 13 now properly enforces this restriction, so we instead mark the enum itself as @available(iOS 13).

Delta/Settings/Cores/MelonDSCoreSettingsViewController.swift

@@ -28,13 +28,12 @@ private extension MelonDSCoreSettingsViewController
         case changeCore
     }
     
+    @available(iOS 13, *)
     enum BIOSError: LocalizedError
     {
         case unknownSize(URL)
         case incorrectHash(URL, hash: String, expectedHash: String)
         case unsupportedHash(URL, hash: String)
-        
-        @available(iOS 13, *)
         case incorrectSize(URL, size: Int, validSizes: Set<ClosedRange<Measurement<UnitInformationStorage>>>)
                 
         private static let byteFormatter: ByteCountFormatter = {