[REV] web: do not use number format in exported group header for floats

Reverts [this commit] because it modified the format of float numbers in
exported xlsx files and we want to avoid introducing an error or
unwanted behavior in version 13, for which support will soon come to an
end.

[this commit]:https://github.com/odoo/odoo/commit/27ab24214dabfafc652280f680f7a650e7d98d2b



closes odoo/odoo#98975

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>