Add alt text to plugin logos (#30710)

public/app/core/components/PageHeader/PageHeader.tsx

@@ -121,7 +121,7 @@ export default class PageHeader extends React.Component<Props, any> {
       <div className="page-header__inner">
         <span className="page-header__logo">
           {main.icon && <Icon name={main.icon as IconName} size="xxxl" className={iconClassName} />}
-          {main.img && <img className="page-header__img" src={main.img} />}
+          {main.img && <img className="page-header__img" src={main.img} alt={`logo of ${main.text}`} />}
         </span>
 
         <div className="page-header__info-block">