Add tests

Author: ahejlsberg

tests/cases/conformance/types/typeRelationships/typeInference/unionAndIntersectionInference3.ts

@@ -0,0 +1,7 @@
+// @strict: true
+
+// Repro from #30720
+
+type Maybe<T> = T | undefined;
+declare function concatMaybe<T>(...args: (Maybe<T> | Maybe<T>[])[]): T[];
+concatMaybe([1, 2, 3], 4);