fix missing the `{% generation %}` keyword while using tokenizer.apply_chat_template(...return_assistant_tokens_mask=True)

chat_template.jinja

@@ -259,6 +259,7 @@
 {%- for message in loop_messages -%}
     {#- At this point only assistant/user/tool messages should remain #}
     {%- if message.role == 'assistant' -%}
+    {% generation %}
         {#- Checks to ensure the messages are being passed in the format we expect #}
         {%- if "content" in message %}
             {%- if "<|channel|>analysis<|message|>" in message.content or "<|channel|>final<|message|>" in message.content %}
@@ -314,6 +315,7 @@
             {{- "<|start|>assistant<|channel|>final<|message|>" + message.content + "<|end|>" }}
             {%- set last_tool_call.name = none %}
         {%- endif %}
+    {% endgeneration %}
     {%- elif message.role == 'tool' -%}
         {%- if last_tool_call.name is none %}
             {{- raise_exception("Message has tool role, but there was no previous assistant message with a tool call!") }}