Toga apps generate warning on macOS 14 (Sonoma)

[freakboy3742]

Describe the bug

Reported by Casimir1965 on Discord.

When running on macOS 14 (Sonoma), Toga apps generate a warning:

2023-11-02 11:10:34.900 Python[83553:21023244] WARNING: Secure coding is not enabled for restorable state! Enable secure coding by implementing NSApplicationDelegate.applicationSupportsSecureRestorableState: and returning YES.

Steps to reproduce

At this point, somewhat unclear. As originally reported, it was "any Toga app"; however, based on this feedback it appears to not affect Toga apps running from the command line.

Based on reading between the lines of the AppKit release notes, the problem may only affect apps deployed with Briefcase.

Expected behavior

No preventable warning is generated by a Toga app.

Screenshots

No response

Environment

• Operating System: macOS 14 (Sonoma)
• Python version: ?
• Software versions:
  • Briefcase: ?
  • Toga: ?

Logs

2023-11-02 11:10:34.900 Python[83553:21023244] WARNING: Secure coding is not enabled for restorable state! Enable secure coding by implementing NSApplicationDelegate.applicationSupportsSecureRestorableState: and returning YES.

Additional context

No response