Fix MathCAT links (#19812)
Summary of the issue:
MathCAT links points to @NSoiffer's GitHub page while it now uses @daisy's one.
As a consequence, the ClearSpeak specification cannot be downloaded and the general MathCAT page is reachable after a redirection.
Description of user facing changes:
ClearSpeak specification can be downloaded again from the link in the User Guide and the MathCAT page is reachable without any redirection when clicking its link in the UG.
