Twenty Twenty-One: Use consistent HTML comments after closing HTML tags.

Follow-up to [45209] for other bundled themes.

Props arcangelini, audrasjb.
Merges [49761] to the 5.6 branch.
Fixes #51950.

git-svn-id: https://develop.svn.wordpress.org/branches/5.6@49827 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentytwentyone/image.php

@@ -99,7 +99,7 @@ while ( have_posts() ) {
 			}
 			?>
 		</footer><!-- .entry-footer -->
-	</article><!-- #post-## -->
+	</article><!-- #post-<?php the_ID(); ?> -->
 	<?php
 	// If comments are open or there is at least one comment, load up the comment template.
 	if ( comments_open() || get_comments_number() ) {

src/wp-content/themes/twentytwentyone/template-parts/content/content-single.php

@@ -41,4 +41,4 @@
 		<?php get_template_part( 'template-parts/post/author-bio' ); ?>
 	<?php endif; ?>
 
-</article><!-- #post-${ID} -->
+</article><!-- #post-<?php the_ID(); ?> -->

src/wp-content/themes/twentytwentyone/template-parts/content/content.php

@@ -43,4 +43,4 @@
 	<footer class="entry-footer default-max-width">
 		<?php twenty_twenty_one_entry_meta_footer(); ?>
 	</footer><!-- .entry-footer -->
-</article><!-- #post-${ID} -->
+</article><!-- #post-<?php the_ID(); ?> -->