Fix media description in various media modals (#8678)

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

@@ -137,6 +137,7 @@ export default class ZoomableImage extends React.PureComponent {
           role='presentation'
           ref={this.setImageRef}
           alt={alt}
+          title={alt}
           src={src}
           style={{
             transform: `scale(${scale})`,