WinForms `background_color` Transparency Fixes #5653

Job	Run time
Pre-commit checks / Pre-commit Checks	38s
Check towncrier / Towncrier Checks	32s
Python package (android) / Create Python Package	52s
Python package (cocoa) / Create Python Package	52s
Python package (demo) / Create Python Package	54s
Python package (core) / Create Python Package	54s
Python package (dummy) / Create Python Package	53s
Python package (gtk) / Create Python Package	47s
Python package (iOS) / Create Python Package	52s
Python package (textual) / Create Python Package	55s
Python package (toga) / Create Python Package	58s
Python package (web) / Create Python Package	42s
Python package (winforms) / Create Python Package	44s
Test core (macos-12, 3.8)	1s
Test core (macos-12, 3.12)	1s
Test core (macos-12, 3.13-dev)	1s
Test core (macos-14, 3.12)	1s
Test core (macos-14, 3.13-dev)	1s
Test core (ubuntu-latest, 3.8)	1m 1s
Test core (ubuntu-latest, 3.12)	1m 8s
Test core (ubuntu-latest, 3.13-dev)	1m 56s
Test core (windows-latest, 3.8)	1m 38s
Test core (windows-latest, 3.12)	1m 53s
Test core (ubuntu-latest, 3.9, false)	1m 6s
Test core (ubuntu-latest, 3.10, false)	1m 13s
Test core (ubuntu-latest, 3.11, false)	1m 0s
Coverage	1s
Testbed	1s
	21m 35s

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