Replace CircleCI with Github Actions. #2

Job	Run time
android-pr / forcehybrid-android	10m 10s
android-pr / forcedroid	14m 28s
android-pr / forcedroid-sfdx	15m 44s
android-pr / forcehybrid-android-sfdx	10m 9s
android-pr / forcereact-android	17m 5s
android-pr / forcereact-android-sfdx	18m 6s
ios-pr / forcehybrid-ios	8m 14s
ios-pr / forcehybrid-ios-sfdx	6m 16s
ios-pr / forceios	13m 18s
ios-pr / forceios-sfdx	8m 22s
ios-pr / forcereact-ios	1h 0m 16s
ios-pr / forcereact-ios-sfdx	33m 24s
	3h 35m 32s

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