[3.14] gh-125225: Fix column misalignment in help('topics') output (gh-125226) (gh-134225)

The 'help("topics")' output was misaligned due to "ASSIGNMENTEXPRESSIONS"
exceeding the implicit maximum default column width of 19 characters.

Reduced the number of columns from 4 to 3 in the listtopics()
function to allow more space for longer topic names.
(cherry picked from commit b22460c44d1bc597c96d4a3d27ad8373d7952820)

Co-authored-by: Étienne Pelletier <EtiennePelletier@users.noreply.github.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>