This allegedly proves that the church decided to change the Bible to give more credence to the Trinity theory.
I find this hypothesis unconvincing for four reasons.
Fourth century Christianity was a mess organizationally, which is why the century was chock full of controversies and councils.
If there was a strong pope figure in the fourth century this theory might be possible, but he would still lack the power and thoroughness to ensure that every last scrap of the original Matthew 28.19 was destroyed.
Before baptism, moreover, the one who baptizes and the one being baptized must fast, and any others who can.