Coding Standards: fix <br/> in core files

[man4toman]

In order to ​self-closing-elements, a single space should precede the self-closing slash.

I created this patch for version 5.0.3, but this version isn't on ticket version selector.

[mukesh27]

Patch.

[mukesh27]

@man4toman, I audited all <br/> occurrences in the following files:

• src/wp-admin/custom-background.php
• src/wp-admin/edit-comments.php
• src/wp-admin/includes/class-wp-filesystem-base.php
• src/wp-admin/includes/class-wp-ms-users-list-table.php
• src/wp-admin/includes/class-wp-plugins-list-table.php
• src/wp-admin/install.php
• src/wp-admin/network/settings.php
• src/wp-admin/network/site-info.php
• src/wp-admin/options-reading.php
• src/wp-includes/widgets/class-wp-widget-archives.php

[mukesh27]

#46105 was marked as a duplicate.