Support array expressions in runs-on (#2088)

* Support array expressions in runs-on

* Simplify appproach to use EvaluateYamlNode, fix case-sensitivity bug

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Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

cmd/platforms.go

@@ -15,7 +15,7 @@ func (i *Input) newPlatforms() map[string]string {
 	for _, p := range i.platforms {
 		pParts := strings.Split(p, "=")
 		if len(pParts) == 2 {
-			platforms[pParts[0]] = pParts[1]
+			platforms[strings.ToLower(pParts[0])] = pParts[1]
 		}
 	}
 	return platforms