Fix issue with referencing the loop variable in a foreach

Fixes: 222160672
Test: go test
Change-Id: I3f9238d4f1684cf4a2d24c4f7f49c832c3f72b97

mk2rbc/expr.go

@@ -595,6 +595,7 @@ func (cx *callExpr) transform(transformer func(expr starlarkExpr) starlarkExpr)
 	for i, arg := range cx.args {
 		argsCopy[i] = arg.transform(transformer)
 	}
+	cx.args = argsCopy
 	if replacement := transformer(cx); replacement != nil {
 		return replacement
 	} else {