Change icons in web UI (#27385)

Co-authored-by: Renaud Chaput <renchap@gmail.com>

app/javascript/mastodon/features/about/index.jsx

@@ -10,6 +10,9 @@ import { List as ImmutableList } from 'immutable';
 import ImmutablePropTypes from 'react-immutable-proptypes';
 import { connect } from 'react-redux';
 
+import { ReactComponent as ChevronRightIcon } from '@material-symbols/svg-600/outlined/chevron_right.svg';
+import { ReactComponent as ExpandMoreIcon } from '@material-symbols/svg-600/outlined/expand_more.svg';
+
 import { fetchServer, fetchExtendedDescription, fetchDomainBlocks  } from 'mastodon/actions/server';
 import Column from 'mastodon/components/column';
 import { Icon  }  from 'mastodon/components/icon';
@@ -73,7 +76,7 @@ class Section extends PureComponent {
     return (
       <div className={classNames('about__section', { active: !collapsed })}>
         <div className='about__section__title' role='button' tabIndex={0} onClick={this.handleClick}>
-          <Icon id={collapsed ? 'chevron-right' : 'chevron-down'} fixedWidth /> {title}
+          <Icon id={collapsed ? 'chevron-right' : 'chevron-down'} icon={collapsed ? ChevronRightIcon : ExpandMoreIcon} /> {title}
         </div>
 
         {!collapsed && (