Finish the OpenGL context for offscreen windows #310

Job	Run time
build-and-test (3.10, ubuntu-latest)	6m 17s
build-and-test (3.10, windows-latest)	4m 24s
build-and-test (3.10, macos-13)	3m 17s
build-and-test (3.10, macos-14)	2m 34s
build-and-test (3.11, ubuntu-latest)	6m 19s
build-and-test (3.11, windows-latest)	4m 1s
build-and-test (3.11, macos-13)	5m 6s
build-and-test (3.11, macos-14)	3m 12s
build-and-test (3.12, ubuntu-latest)	6m 32s
build-and-test (3.12, windows-latest)	5m 45s
build-and-test (3.12, macos-13)	7m 30s
build-and-test (3.12, macos-14)	3m 4s
	58m 1s

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