AppKit macOS xcode15.0 b6

#AppKit.framework https://github.com/xamarin/xamarin-macios/pull/18762

diff -ruN /Applications/Xcode_15.0.0-beta5.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSGradient.h /Applications/Xcode_15.0.0-beta6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSGradient.h
--- /Applications/Xcode_15.0.0-beta5.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSGradient.h	2023-07-19 03:39:34
+++ /Applications/Xcode_15.0.0-beta6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSGradient.h	2023-08-04 04:29:46
@@ -71,8 +71,7 @@
 */
 - (nullable instancetype)initWithColors:(NSArray<NSColor *> *)colorArray atLocations:(nullable const CGFloat *)locations colorSpace:(NSColorSpace *)colorSpace NS_DESIGNATED_INITIALIZER;
 
-- (instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
-
+- (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
 
 /* DRAWING LINEAR GRADIENTS */