Fix fdo#80433 help pages for new T functions

T.DIST, T.DIST.2T, T.DIST.RT, T.INV, T.INV.2T and T.TEST

Change-Id: I65fc995e0131cfcc528d64984ceafed25cd74fbc
Reviewed-on: https://gerrit.libreoffice.org/10426
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>