Is a pledge not to speak of matters that do not concern me, and then returning to speak of them, considered a vow, and will Allah forgive me for that?

One should not delve into matters that do not concern him, based on the Prophet's (peace be upon him) saying: "Among the excellence of a person's Islam is his leaving alone that which does not concern him." If the speech is not forbidden, then it is contrary to what is better and not a sin, but it diminishes the excellence of a person's Islam. Praying to Allah to protect you is a good thing, and saying "I will not speak about those topics again" is not a vow. Speaking about matters that do not concern one is not a sin that necessitates seeking forgiveness. Nevertheless, one who repents from a sin is like one who has no sin.