fix: update condition for default value assignment in BaseModel template

Author: koxudaxi

src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2

@@ -32,7 +32,7 @@ class {{ class_name }}({{ base_class }}):{% if comment is defined %}  # {{ comme
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
     {%- endif %}
-    {%- if not field.required and (field.represented_default != 'None' or not field.strip_default_none) or field.data_type.is_optional)
+    {%- if not field.required and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}