blocks: Fix cpuparticles2d_finished missing code template

Author: dylanmccall

addons/block_code/blocks/spawn/cpuparticles2d_finished.tres

@@ -11,7 +11,7 @@ category = "Lifecycle | Spawn"
 type = 1
 variant_type = 0
 display_template = "when particles are finished"
-code_template = ""
+code_template = "func _on_finished():"
 defaults = {}
 signal_name = "finished"
 scope = ""