Merge pull request #611 from larskanis/close-prepared #751

Job	Run time
Build	5s
Build	5s
Test (windows, head, 17.0-1-windows-x64, 17)	5m 59s
Test (windows, head, 17.0-1-windows-x64, 17)	5m 59s
Test (windows, 2.7, 10.20-1-windows-x64, 10)	6m 8s
Test (windows, 2.7, 10.20-1-windows-x64, 10)	6m 8s
Test (windows, mswin, 17.0-1-windows-x64, 17)	4m 34s
Test (windows, mswin, 17.0-1-windows-x64, 17)	4m 34s
Test (ubuntu, head, 17)	1m 6s
Test (ubuntu, head, 17)	1m 6s
Test (ubuntu, 3.2, 12)	1m 13s
Test (ubuntu, 3.2, 12)	1m 13s
Test (ubuntu, 20.04, 2.7, 10)	1m 32s
Test (ubuntu, 20.04, 2.7, 10)	1m 32s
Test (ubuntu, truffleruby, 13)	1m 28s
Test (ubuntu, truffleruby, 13)	1m 28s
Test (ubuntu, truffleruby-head, 17)	1m 53s
Test (ubuntu, truffleruby-head, 17)	1m 53s
Test (macos, head, 17.0-1-osx, 17)	1m 18s
Test (macos, head, 17.0-1-osx, 17)	6h 0m 20s
	6h 49m 34s

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