Widgets: Replace http with https in the link placeholder widget image

The existing placeholder can make the user think that they must use http. We should encourage the use of https. 
Also, the block editor uses https for its placeholders. Let's add some consistency.

Props Chaton666, audrasjb, mukesh27.
Fixes #46320.


git-svn-id: https://develop.svn.wordpress.org/trunk@45777 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/widgets/class-wp-widget-media-image.php

@@ -335,7 +335,7 @@ public function render_control_template_scripts() {
 			<# if ( data.url ) { #>
 			<p class="media-widget-image-link">
 				<label for="{{ elementIdPrefix }}linkUrl"><?php esc_html_e( 'Link to:' ); ?></label>
-				<input id="{{ elementIdPrefix }}linkUrl" type="text" class="widefat link" value="{{ data.link_url }}" placeholder="http://" pattern="((\w+:)?\/\/\w.*|\w+:(?!\/\/$)|\/|\?|#).*">
+				<input id="{{ elementIdPrefix }}linkUrl" type="text" class="widefat link" value="{{ data.link_url }}" placeholder="https://" pattern="((\w+:)?\/\/\w.*|\w+:(?!\/\/$)|\/|\?|#).*">
 			</p>
 			<# } #>
 		</script>