The problem is the calls to Marshal.ReadInt16() and Marshal.ReadInt32() inside the TestSystem.CopyDataFormat1 method. In some versions of Unity, those two calls end up calling System.Buffer.InternalMemcpy, which is unavailable to Burst. The fix is to replace Marshal.ReadInt16() and Marshal.ReadInt32() with custom implementations of those two methods.
The error message "unable to find internal function..." is admittedly unhelpful, since it doesn't point to the code that caused the problem and thus isn't actionable. We have this in our backlog as something we want to improve.