Fixed `App.current_window` on macOS, for when a dialog is in focus #7035

Job	Run time
Pre-commit checks / Pre-commit Checks	41s
Check towncrier / Towncrier Checks	32s
Package Toga (android) / Create Python Package	14s
Package Toga (cocoa) / Create Python Package	26s
Package Toga (core) / Create Python Package	21s
Package Toga (demo) / Create Python Package	23s
Package Toga (dummy) / Create Python Package	14s
Package Toga (gtk) / Create Python Package	24s
Package Toga (iOS) / Create Python Package	23s
Package Toga (textual) / Create Python Package	15s
Package Toga (toga) / Create Python Package	23s
Package Toga (winforms) / Create Python Package	24s
Package Toga (web) / Create Python Package	14s
Test core (macos-latest, 3.9)	47s
Test core (macos-latest, 3.10)	44s
Test core (macos-latest, 3.11)	1m 6s
Test core (macos-latest, 3.12)	1m 1s
Test core (macos-latest, 3.13)	51s
Test core (ubuntu-latest, 3.9)	55s
Test core (ubuntu-latest, 3.10)	48s
Test core (ubuntu-latest, 3.11)	57s
Test core (ubuntu-latest, 3.12)	59s
Test core (ubuntu-latest, 3.13)	1m 14s
Test core (windows-latest, 3.9)	1m 40s
Test core (windows-latest, 3.10)	1m 45s
Test core (windows-latest, 3.11)	1m 56s
Test core (windows-latest, 3.12)	1m 53s
Test core (windows-latest, 3.13)	2m 22s
Coverage	35s
Testbed (macOS-x86_64)	4m 57s
Testbed (macOS-arm64)	3m 40s
Testbed (windows)	5m 33s
Testbed (linux-x11)	3m 16s
Testbed (linux-wayland)	3m 40s
Testbed (android)	8m 16s
Testbed (iOS)	16m 49s
Testbed (textual-linux)	52s
Testbed (textual-macOS)	1m 0s
Testbed (textual-windows)	2m 20s
	1h 14m 50s

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