Update docs page introduction_to_3d to accurately explain Transform3D

[Skyefre]

As mentioned in Issue #8904, a Transform3D is a 3x4 matrix, not a 4x3. This simply updates line 35 in introduction_to_3d.rst to match.

edit: I did not mean to try to merge 99 commits, I only wanted to request merge the one that I was making, and I'm afraid that I messed up.

[mhilbrunner]

You probably started your PR branch from either an outdated version of the repo's master branch or another branch entirely. Fetching the updated upstream branches and then rebasing your PR branch on the current master commit should fix this (and will a force-push afterwards). Make a backup of your changes before, just to be safe. If you need assistance, feel free to poke us on the #documentation channel on the contributor Rocketchat (link, we are happy to help and Git can be a bit of a, well git. :)

[Skyefre]

I followed your instructions and believe that I fixed the issue, thank you! Please let me know if there is anything further I need to do

[AThousandShips]

You haven't fixed it fully, there's still incorrect commits in it, please do git rebase -i master and put "drop" in front of bc4d39d and 19952ec :)

[Skyefre]

Ok ok I believe it should finally be good now, unless 3b877c8 is getting in the way of anything. Thank you!

[AThousandShips]

Still got the wrong versions, you need to do the git rebase again and then do git push -f, you merged your local branch into the upstream

[Skyefre]

how about now?

[mhilbrunner]

Thank you, it indeed looks perfect now :) Congrats on your first merged contribution to Godot's docs! 🎉

[Skyefre]

thank you for your assistance :)

[mhilbrunner]

Cherry-picked to 4.2 in #9648.