Add MINGW package dependency which is resolved by RubyInstaller #815

Job	Run time
Build	3s
Test (windows, head, 17.0-1-windows-x64, 17)	5m 43s
Test (windows, 2.7, 10.20-1-windows-x64, 10)	9m 41s
Test (windows, mswin, 17.0-1-windows-x64, 17)	4m 47s
Test (ubuntu, head, 17)	1m 9s
Test (ubuntu, 3.2, 12)	1m 23s
Test (ubuntu, 20.04, 2.7, 10)	1m 30s
Test (ubuntu, truffleruby, 14)	1m 46s
Test (ubuntu, truffleruby-head, 17)	1m 58s
Test (macos, head, 17.0-1-osx, 17)	1m 16s
	29m 16s

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