[findbugs] ProgressReportingFilter can be a static inner class

Change-Id: I628b1f25f04c9297655d5ac451ae5a133db53896
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java

@@ -82,7 +82,7 @@ import org.eclipse.jgit.treewalk.filter.TreeFilter;
  */
 public class IndexDiff {
 
-	private final class ProgressReportingFilter extends TreeFilter {
+	private static final class ProgressReportingFilter extends TreeFilter {
 
 		private final ProgressMonitor monitor;