Issue #2203: Fix RedundantModifier check at final classes in interfaces

src/main/java/com/puppycrawl/tools/checkstyle/checks/modifier/RedundantModifierCheck.java

@@ -228,7 +228,8 @@ public class RedundantModifierCheck
                         && ast.getType() != TokenTypes.METHOD_DEF
                 || type == TokenTypes.ABSTRACT
                         && ast.getType() != TokenTypes.CLASS_DEF
-                || type == TokenTypes.FINAL) {
+                || type == TokenTypes.FINAL
+                        && ast.getType() != TokenTypes.CLASS_DEF) {
                 log(modifier.getLineNo(), modifier.getColumnNo(),
                         MSG_KEY, modifier.getText());
                 break;

src/test/resources/com/puppycrawl/tools/checkstyle/InputNestedClassInPublicInterfaceRedundantModifiers.java

@@ -42,4 +42,9 @@ public interface InputNestedClassInPublicInterfaceRedundantModifiers {
                         }
                 }
         }
+        final class FinalNestedClassInInterface {
+                interface InnerInterface {
+                        final class FinalNestedClassInNestedInterface {}
+                }
+        }
 }