[ticket/12284] Improve readability of extension manager details

Use span tags like the rest of the ACP does, instead of P tags.
There is no semantic need to use P tags here. These are not
paragraphs.

PHPBB3-12284
Merge remote-tracking branch 'VSEphpbb/ticket/12284' into develop

* VSEphpbb/ticket/12284:
  [ticket/12284] Improve readability of extension manager details