My understanding is that I still own the copyright on the work but am I required to provide them the scripts that I made to generate the artwork? Can they then run the script again and claim the output as a new work?
The GPL FAQ answers this pretty directly:
Can I use GPL-covered editors such as GNU Emacs to develop nonfree programs? Can I use GPL-covered tools such as GCC to compile them? (#CanIUseGPLToolsForNF)
Yes, because the copyright on the editors and tools does not cover the code you write. Using them does not place any restrictions, legally, on the license you use for your code.
... nor would it place any restriction on a graphical artwork you create. (At least as long as your image doesn't show code from blender's code base)
This is nothing very special: writing a thesis or a book in MS word does not give Microsoft any rights in the text, and the author can license (sell) it under whatever conditions they like to whomever they want to license it to.
You can also use git (which is distributed under GPL) to version control code that is under any kind of GPL-incompatible license.
Any software license claiming rights on what you produce using that software (as opposed to changing/adapting the code of the software and distributing the derived software) would be rather impractical:
Who should then have what rights if a book were written in emacs using git for version control and then be typeset in LaTeX, possibly on a Linux system. And I didn't even mention the file system and so on...
The point where GPL would kick in is if you'd decide to make and distribute a software to generate such artwork by linking your scripts together with blender's code: that would need to be under GPL.
In contrast, if you'd distribute your scripts only ("to be run in blender"), you're free to choose whatever license you like.
Like you can distribute any python script you write under whatever license you choose - the license of the python program to run the script with doesn't matter.
That the software is under the GPL does not place any scripts written for it under the GPL, nor any output. The script was a tool used to create the image. he creator has copyright until/unless it is lawfully transfered to someone else. The creator is no more required to hand over the script along with the image than an oil painter is required to hand over the brush used along with a painting.