Is the Hadith by Ibn Abi Shaybah about Yazid ibn..., which tells of finding the grave of Umm al-Mu'minin Habibah and building a room over it, fabricated, and why?

Building upon graves is forbidden because it is a means to polytheism (shirk) and an innovation (bid'ah). The argument that the grave of Umm Habiba had a structure upon it, based on a corrupt narration by 'Abd al-'Aziz ibn 'Imran — who is abandoned in Hadith and whose narrations are rejected by the Imams — is not valid. Indeed, the graves of the Companions in Al-Baqi' have no structures upon them.