test: cover negative fib numbers

Author: ParanoidUser

kata/3-kyu/the-millionth-fibonacci-kata/test/FibonacciTest.java

@@ -13,6 +13,7 @@ class FibonacciTest {
       3, 2
       4, 3
       5, 5
+      -6, -8
       """)
   void sample(BigInteger input, BigInteger expected) {
     assertEquals(expected, Fibonacci.fib(input));