Fix style of legacy column headers (#6342)

* Fix regression from #6199: Style of legacy column headers

* Fix tests

* Clean up variables

app/javascript/mastodon/features/ui/components/__tests__/column-test.js

@@ -21,13 +21,13 @@ describe('<Column />', () => {
           <div className='scrollable' />
         </Column>
       );
-      wrapper.find(ColumnHeader).simulate('click');
+      wrapper.find(ColumnHeader).find('button').simulate('click');
       expect(global.requestAnimationFrame.mock.calls.length).toEqual(1);
     });
 
     it('does not try to scroll if there is no scrollable content', () => {
       const wrapper = mount(<Column heading='notifications' />);
-      wrapper.find(ColumnHeader).simulate('click');
+      wrapper.find(ColumnHeader).find('button').simulate('click');
       expect(global.requestAnimationFrame.mock.calls.length).toEqual(0);
     });
   });

app/javascript/mastodon/features/ui/components/column_header.js

 import React from 'react';
 import PropTypes from 'prop-types';
+import classNames from 'classnames';
 
 export default class ColumnHeader extends React.PureComponent {
 
@@ -16,19 +17,20 @@ export default class ColumnHeader extends React.PureComponent {
   }
 
   render () {
-    const { type, active, columnHeaderId } = this.props;
+    const { icon, type, active, columnHeaderId } = this.props;
+    let iconElement = '';
 
-    let icon = '';
-
-    if (this.props.icon) {
-      icon = <i className={`fa fa-fw fa-${this.props.icon} column-header__icon`} />;
+    if (icon) {
+      iconElement = <i className={`fa fa-fw fa-${icon} column-header__icon`} />;
     }
 
     return (
-      <div role='button heading' tabIndex='0' className={`column-header ${active ? 'active' : ''}`} onClick={this.handleClick} id={columnHeaderId || null}>
-        {icon}
-        {type}
-      </div>
+      <h1 className={classNames('column-header', { active })} id={columnHeaderId || null}>
+        <button onClick={this.handleClick}>
+          {iconElement}
+          {type}
+        </button>
+      </h1>
     );
   }