Fix editor Parallax2D grid snap movement

[markdibarry]

Closes #97601

As far as I can see the editor avoids updating the position when grid snap is on because it sends multiple of the same value causing an early return. I think that guard should be there in most cases, but in the editor it makes sense to remove.

2025-01-19.13-40-59.mp4

[Mickeon]

Not using set_scroll_offset directly feels a bit odd to me, as the added code is the same minus the early return. This is still a decent solution, so perhaps it's worth commenting on why this is done?

[Repiteo]

Thanks!