Fix argument exception

lib/src/widgets/raw_editor/raw_editor_state.dart

@@ -808,6 +808,13 @@ class QuillRawEditorState extends EditorState
           return defaultStyles!.h2!.verticalSpacing;
         case 3:
           return defaultStyles!.h3!.verticalSpacing;
+        case 4:
+          return defaultStyles!.h4!.verticalSpacing;
+        case 5:
+          return defaultStyles!.h5!.verticalSpacing;
+        case 6:
+          return defaultStyles!.h6!.verticalSpacing;
+
         default:
           throw ArgumentError('Invalid level $level');
       }

lib/src/widgets/text_block.dart

@@ -312,6 +312,18 @@ class EditableTextBlock extends StatelessWidget {
           top = defaultStyles!.h3!.verticalSpacing.top;
           bottom = defaultStyles.h3!.verticalSpacing.bottom;
           break;
+        case 4:
+          top = defaultStyles!.h4!.verticalSpacing.top;
+          bottom = defaultStyles.h4!.verticalSpacing.bottom;
+          break;
+        case 5:
+          top = defaultStyles!.h5!.verticalSpacing.top;
+          bottom = defaultStyles.h5!.verticalSpacing.bottom;
+          break;
+        case 6:
+          top = defaultStyles!.h6!.verticalSpacing.top;
+          bottom = defaultStyles.h6!.verticalSpacing.bottom;
+          break;
         default:
           throw ArgumentError('Invalid level $level');
       }