fix tk error on windows

scheduling/sigmas_graph.py

@@ -3,6 +3,10 @@ import random
 
 from comfy_api.latest import io, ui
 import folder_paths
+
+import matplotlib
+matplotlib.use("Agg")
+
 import matplotlib.pyplot as plt
 import matplotlib.ticker as ticker
 import numpy as np
@@ -10,6 +14,7 @@ from PIL import Image
 import torch
 
 
+
 class SigmasGraph(io.ComfyNode):
     def __init__(self):
         # Based on PreviewImage logic here to save to the temp directory