Fix T98919: Eevee unlinked aov output nodes don't render.

Eevee rendered an empty image for aov nodes that weren't linked to
any other nodes. When connected the result was OK. The root cause was
that the AOV nodes were not marked as output node and pruned when not
connected to any other nodes. The pruning process is there to reduce
the complexity of the GLSL and improve compilation time and
execution time.

source/blender/nodes/shader/node_shader_tree.cc

@@ -1007,6 +1007,7 @@ static void ntree_shader_pruned_unused(bNodeTree *ntree, bNode *output_node)
 
   LISTBASE_FOREACH (bNode *, node, &ntree->nodes) {
     if (node->type == SH_NODE_OUTPUT_AOV) {
+      node->tmp_flag = 1;
       nodeChainIterBackwards(ntree, node, ntree_branch_node_tag, nullptr, 0);
     }
   }