No person who is incompetent under section 5922 (relating to disqualification by perjury), section 5923 (relating to confidential communications between spouses), section 5924 (relating to spouses as witnesses against each other) and section 5928 (relating to confidential communications to attorney) shall become competent by the general language of section 5930 (relating to surviving party as witness, in case of death, mental incapacity, etc.).