Clean up rake file and use correct extension on Windows. #3

Job	Run time
test-windows (3.2)	39s
lint	5s
test-macos (3.2)	7s
test-macos (3.3)	7s
test-windows (3.1)	44s
test-linux (3.3)	7s
cmake-build (windows-latest, msvc-release)	53s
test-windows (3.3)	40s
cmake-build (macos-latest, macos-release)	11s
test-macos (3.1)	7s
test-linux (3.0)	5s
test-linux (3.2)	8s
test-linux (3.1)	6s
cmake-build (ubuntu-latest, linux-release)	14s
	4m 13s

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