Each time when rendering an image a new context is created. When the
context is destroyed it can still contain a render graph, which ownership
isn't transferred back to the device. Resulting in an increase of several
MB per render. The render graph is cleanly destroyed during quiting as
there is a master list of created render graphs.
Fixed by moving the ownership of the render graph back to the device
when a context is unregistered.
Pull Request: https://projects.blender.org/blender/blender/pulls/138095
f6a8993570