--- a/wp/wp-includes/customize/class-wp-customize-header-image-control.php	Tue Dec 15 15:52:01 2020 +0100
+++ b/wp/wp-includes/customize/class-wp-customize-header-image-control.php	Wed Sep 21 18:19:35 2022 +0200
@@ -133,7 +133,7 @@
 				data-customize-image-value="{{{data.header.url}}}"
 				data-customize-header-image-data="{{JSON.stringify(data.header)}}">
 				<span class="screen-reader-text"><?php _e( 'Set image' ); ?></span>
-				<img src="{{{data.header.thumbnail_url}}}" alt="{{{data.header.alt_text || data.header.description}}}">
+				<img src="{{{data.header.thumbnail_url}}}" alt="{{{data.header.alt_text || data.header.description}}}" />
 			</button>
 
 			<# if ( data.type === 'uploaded' ) { #>