fix: update correct metric in batch_embed_thumbnail (#22501)

batch_embed_thumbnail processes image thumbnails but reports timing
to text_inference_speed instead of image_inference_speed.

frigate/embeddings/embeddings.py

@@ -266,7 +266,7 @@ class Embeddings:
             )
 
         duration = datetime.datetime.now().timestamp() - start
-        self.text_inference_speed.update(duration / len(valid_ids))
+        self.image_inference_speed.update(duration / len(valid_ids))
 
         return embeddings