Test stability: add fsTick() to avoid random testPruneNone() failures

At least on Windows the test failed each second time on the last assert.
Adding a small timeout before gc.prune() makes the test stable again.

Change-Id: I23d98dd565912c58dcf2f24f3ebc24824670cff3
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/GcReflogTest.java

@@ -75,6 +75,7 @@ public class GcReflogTest extends GcTestCase {
 		tr.blob("x");
 		stats = gc.getStatistics();
 		assertEquals(9, stats.numberOfLooseObjects);
+		fsTick();
 		gc.prune(Collections.<ObjectId> emptySet());
 		stats = gc.getStatistics();
 		assertEquals(8, stats.numberOfLooseObjects);