Add failing test for no unreachable statement not in allowlist

Author: owen-mc

go/ql/test/query-tests/RedundantCode/UnreachableStatement/UnreachableStatement.expected

@@ -11,3 +11,4 @@
 | main.go:153:2:153:22 | return statement | This statement is unreachable. |
 | main.go:159:2:159:43 | return statement | This statement is unreachable. |
 | main.go:171:2:171:14 | expression statement | This statement is unreachable. |
+| main.go:177:1:178:12 | labeled statement | This statement is unreachable. |

go/ql/test/query-tests/RedundantCode/UnreachableStatement/main.go

@@ -171,6 +171,13 @@ func test21() {
 	unreachable() // $ Alert
 }
 
+func test22() {
+	goto reachableLabel
+	panic("unreachable") // OK: allowlisted statement
+reachableLabel:
+	reachable() // $ SPURIOUS: Alert // OK: reachable through the goto
+}
+
 func test23() {
 	if true {
 		return