Help/About: Add `/` character to `<img>` and `<source>` tags.

While this has no effect on void elements in HTML5, it fixes a minor inconsistency with the rest of core.

Follow-up to [47493], [48834], [50556], [51418].

Props radixweb, ankitmaru, TobiasBg, sabernhardt, audrasjb.
Fixes #53716.
Built from https://develop.svn.wordpress.org/trunk@51473


git-svn-id: http://core.svn.wordpress.org/trunk@51084 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/about.php

@@ -160,8 +160,8 @@ require_once ABSPATH . 'wp-admin/admin-header.php';
 			</h2>
 			<div class="column about__image is-vertically-aligned-center">
 				<picture>
-					<source srcset="https://s.w.org/images/core/5.8/about-theme-json.png, https://s.w.org/images/core/5.8/about-theme-json-2x.png 2x">
-					<img src="https://s.w.org/images/core/5.8/about-theme-json.png" alt="">
+					<source srcset="https://s.w.org/images/core/5.8/about-theme-json.png, https://s.w.org/images/core/5.8/about-theme-json-2x.png 2x" />
+					<img src="https://s.w.org/images/core/5.8/about-theme-json.png" alt="" />
 				</picture>
 			</div>
 		</div>

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51472';
+$wp_version = '5.9-alpha-51473';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.