Tests

Add messagebox extension windows support #78

Job	Run time
Tests (8.4, ubuntu-latest, prefer-stable)	18s
Tests (8.5, ubuntu-latest, prefer-stable)	15s
Tests (8.4, windows-latest, prefer-stable)	50s
Tests (8.4, windows-latest, prefer-lowest)	38s
Tests (8.5, ubuntu-latest, prefer-lowest)	24s
Tests (8.4, macos-latest, prefer-lowest)	3m 53s
Tests (8.5, macos-latest, prefer-lowest)	2m 42s
Tests (8.5, macos-latest, prefer-stable)	2m 56s
Tests (8.5, windows-latest, prefer-stable)	1m 5s
Tests (8.5, windows-latest, prefer-lowest)	41s
Tests (8.4, ubuntu-latest, prefer-lowest)	12s
Tests (8.4, macos-latest, prefer-stable)	2m 34s
	16m 28s

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