PHP 8.3+ highlight_string changes affect content styling

[AllenJB]

From UPGRADING:

. The resultant HTML of highlight_string and highlight_file has changed.
Whitespace between outer HTML tags is removed. Newlines and spaces
are no longer converted to HTML entities. The whole HTML is now wrapped in
<pre> tag. The outer <span> has been merged with <code>.

This has altered the styling of highlighted PHP code (most noticeably the padding around code blocks has been lost) in both the XHTML and Web formats.

[AllenJB]

See php/web-php#1501