add testing.FailNow and related function to unreachable check

[Abirdcfly]

Is your feature request related to a problem? Please describe.

A simplified code is as follows:

func TestA(t *testing.T) {
	tests := make([]int, 100)
	for i := range tests {
		println("i: ", i)
		if i == 0 {
			t.Fatal("i == 0") // MATCH /unreachable code after this statement/
			println("unreachable")
			continue
		}
		if i == 1 {
			t.Fatalf("i:%d", i) // MATCH /unreachable code after this statement/
			println("unreachable")
			continue
		}
		if i == 2 {
			t.FailNow() // MATCH /unreachable code after this statement/
			println("unreachable")
			continue
		}
		/*  Skip is used to temporarily skip tests. The code following it is intentionally unreachable.
			if i == 3 {
				t.Skip("i == 3") // MATCH /unreachable code after this statement/
				println("unreachable")
				continue
			}
			if i == 4 {
				t.Skipf("i:%d", i) // MATCH /unreachable code after this statement/
				println("unreachable")
				continue
			}
			if i == 5 {
				t.SkipNow() // MATCH /unreachable code after this statement/
				println("unreachable")
				continue
			}
		*/
	}
}

The actual code can be seen in k8s https://github.com/kubernetes/kubernetes/pull/111228/files#diff-b5b428649cab55e247eddbd00bc278c628c40ed524814ffe9dede44af19ee3b5R1899 and etcd etcd-io/etcd#14235

Describe the solution you'd like
I wish there was a way to detect them

Describe alternatives you've considered
Goland can detect them, but has bug in some situation, see https://youtrack.jetbrains.com/issue/GO-13383

go vet cant detect this. Some discussions are here golang/go#53968

Additional context
None