ReachabilityCheckerTestCase: fix reachable from self test case

Change-Id: I8f94a0a0ff401f1691b3757002756b4e83dd8640
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/ReachabilityCheckerTestCase.java

@@ -88,7 +88,7 @@ public abstract class ReachabilityCheckerTestCase
 		assertReachable("reachable from another tip",
 				checker.areAllReachable(Arrays.asList(a), Stream.of(b2)));
 		assertReachable("reachable from itself",
-				checker.areAllReachable(Arrays.asList(a), Stream.of(b2)));
+				checker.areAllReachable(Arrays.asList(a), Stream.of(a)));
 	}
 
 	@Test