LongObjectIdTest: Add back self comparison test

The test was removed in 4886621 to prevent a warning from
error-prone.

Add it back but rewrite it in a way that does not cause the
warning.

This reverts commit 4886621261.

Change-Id: Id3994e2d882a9d08bf548b7778406f8a80fbf830
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit.lfs.test/tst/org/eclipse/jgit/lfs/lib/LongObjectIdTest.java

@@ -291,6 +291,8 @@ public class LongObjectIdTest {
 				"0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef");
 		assertEquals(0, id1.compareTo(LongObjectId.fromString(
 				"0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef")));
+		AnyLongObjectId self = id1;
+		assertEquals(0, id1.compareTo(self));
 
 		assertEquals(-1, id1.compareTo(LongObjectId.fromString(
 				"1123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef")));