hidden_activation -> hidden_act

This is the config value name for the copied MLP layer

config.json

@@ -24,7 +24,7 @@
   "transformers_version": "4.45.0.dev0",
   "vision_config": {
     "head_dim": 64,
-    "hidden_activation": "gelu",
+    "hidden_act": "gelu",
     "image_size": 1024,
     "model_type": "pixtral",
     "patch_size": 16,