Add MINGW package dependency which is resolved by RubyInstaller #814

Job	Run time
Build	4s
Test (windows, head, 17.0-1-windows-x64, 17)	6m 2s
Test (windows, 2.7, 10.20-1-windows-x64, 10)	7m 19s
Test (windows, mswin, 17.0-1-windows-x64, 17)	5m 2s
Test (ubuntu, head, 17)	1m 8s
Test (ubuntu, 3.2, 12)	1m 16s
Test (ubuntu, 20.04, 2.7, 10)	1m 29s
Test (ubuntu, truffleruby, 14)	1m 41s
Test (ubuntu, truffleruby-head, 17)	1m 56s
Test (macos, head, 17.0-1-osx, 17)	1m 26s
	27m 23s

Provide feedback