[ticket/12491] Fix clashing USERNAME_FULL template variable.

The user notes and user warn pages have a variable with the same name.

PHPBB3-12491
Merge pull request #2409 from prototech/ticket/12491

[ticket/12491] Fix clashing USERNAME_FULL template variable.

* prototech/ticket/12491:
  [ticket/12491] Fix clashing USERNAME_FULL template variable.