Fix `PushToHubCallback` import in Share a model docs (#21457)

docs: update PushToHubCallback import in docs

docs/source/de/model_sharing.mdx

@@ -146,7 +146,7 @@ Geben Sie ein Modell mit [`PushToHubCallback`] an den Hub weiter. In der [`PushT
 - Die `hub_model_id`, die Ihr Hub-Benutzername und Modellname ist.
 
 ```py
->>> from transformers.keras.callbacks import PushToHubCallback
+>>> from transformers import PushToHubCallback
 
 >>> push_to_hub_callback = PushToHubCallback(
 ...     output_dir="./your_model_save_path", tokenizer=tokenizer, hub_model_id="your-username/my-awesome-model"

docs/source/en/model_sharing.mdx

@@ -146,7 +146,7 @@ Share a model to the Hub with [`PushToHubCallback`]. In the [`PushToHubCallback`
 - The `hub_model_id`, which is your Hub username and model name.
 
 ```py
->>> from transformers.keras.callbacks import PushToHubCallback
+>>> from transformers import PushToHubCallback
 
 >>> push_to_hub_callback = PushToHubCallback(
 ...     output_dir="./your_model_save_path", tokenizer=tokenizer, hub_model_id="your-username/my-awesome-model"

docs/source/es/model_sharing.mdx

@@ -139,7 +139,7 @@ Los usuarios de TensorFlow pueden activar la misma funcionalidad con [`PushToHub
 - El `hub_model_id`, el cual es tu usuario Hub y el nombre del modelo.
 
 ```py
->>> from transformers.keras.callbacks import PushToHubCallback
+>>> from transformers import PushToHubCallback
 
 >>> push_to_hub_callback = PushToHubCallback(
 ...     output_dir="./your_model_save_path", tokenizer=tokenizer, hub_model_id="your-username/my-awesome-model"

docs/source/it/model_sharing.mdx

@@ -150,7 +150,7 @@ Condividi un modello nell'Hub con [`PushToHubCallback`]. Nella funzione [`PushTo
 - L'`hub_model_id`, che è il tuo username sull'Hub e il nome del modello.
 
 ```py
->>> from transformers.keras.callbacks import PushToHubCallback
+>>> from transformers import PushToHubCallback
 
 >>> push_to_hub_callback = PushToHubCallback(
 ...     output_dir="./il_path_dove_salvare_il_tuo_modello",