Blender Git Loki

Depsgraph: release GIL when evaluating the depsgraph

Evaluating the dependency graph potentially executes Python code when
evaluating drivers. In specific situations (see T91046) this could deadlock
Blender entirely. Temporarily releasing the GIL when evaluating the depsgraph
resolves this.

Calling the `BPy_BEGIN_ALLOW_THREADS` macro is relatively safe, as it's
a no-op when the current thread does not have the GIL.

Developed in collaboration with @sergey

Manifest task: T91046