Fixes#1656
When called as part of window restoration AppKit has a lock, so
NSAppearance changes need to be called async.
See deadlock:
```
Thread 1 Queue : com.apple.main-thread (serial)
0 0x000000018fd63fac in __ulock_wait ()
1 0x00000001069bf720 in _dlock_wait ()
2 0x00000001069bfaec in _dispatch_group_wait_slow ()
3 0x0000000106b5f5c4 in interposed_dispatch_group_wait ()
4 0x00000001937fb1f0 in NSCGSTransactionRunPreCommitActions_ ()
5 0x00000001938f1230 in -[_NSCGSTransaction synchronize] ()
6 0x00000001938f11ac in NSCGSTransactionSynchronize ()
7 0x000000019382ad30 in +[NSCGSWindow(NSCGSSpace) isAnyWindowOnAVisibleSpace:] ()
8 0x000000019382a968 in -[NSWindow _isInSomeVisibleSpace] ()
9 0x000000019382a8e4 in -[NSWindow isOnActiveSpace] ()
10 0x0000000193db8d98 in -[NSApplication(NSApplicationAppearance_Internal) _invalidateWindowAppearances] ()
11 0x00000001938f44d4 in -[NSApplication(NSAppearanceCustomization) setAppearance:] ()
12 0x0000000102c48050 in AppDelegate.syncAppearance() at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:412
13 0x0000000102c47840 in AppDelegate.configDidReload(_:) at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:380
14 0x0000000102c43c7c in AppDelegate.applicationDidFinishLaunching(_:) at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:110
```
Fixes#1389
This is just a fun AppKit quirk. This menu item is set automatically
based on the keyboard shortcut (apparently) and when its overwritten
then its gone forever. So, let's just not set it.
