The Gemorah does not mention this as a source. The mishna (?????? ?.)says ????? ????? ????? ?????? ??? ?????. the Gemorah asks ????? ???? (how do we know this) Rashi explains ????? ?????? ????? (that ladies are not allowed to testify) and the Gemeorah answers that the ???? says ????? ??? ?????? (the two men stand)this teaches us that men testify, not women.
In certain cases where the judge finds the woman more credible he can accept her testimony regarding certain matters, see ?????? ??
??? ??? ?? ??? ??? ?? ???? ?? ?? ???? ??? ?? ????? ?? ?? ??? ?? ??????(the Amora Rava accepted the testimony of the daughter of Rav Chisda, which he knew to be credible, despite not accepting similar testimony from the well know scholar Rav Papa )
Also in a case of ??? ????? where it is clear to bais din that there are witnesses lying, it is forbidden to rule base on male witnesses. So if women contradict male witnesses this would very often fall into such a category.
Women are technically ???? ????? however it doesn’t mean they have no credibility in Bais Din.
When it comes to Agunos women are also believed.
And of course for all matters pertaining to regular prohibitions (?? ??? ????????)they are believed.