Documentation Mismatch for Testing API Calls with Django

**What is the current behavior?**
The documentation for testing API calls with Django on the official website of [Graphene-Django](https://docs.graphene-python.org/projects/django/en/latest/testing/) shows incorrect usage of a parameter named **op_name** in the code examples for unit tests and pytest integration. However, upon inspecting the corresponding documentation in the [GitHub repository](https://github.com/graphql-python/graphene-django/blob/main/docs/testing.rst), the correct parameter operation_name is used.

**Steps to Reproduce**

Visit the [Graphene-Django](https://docs.graphene-python.org/projects/django/en/latest/testing/) documentation website's section on testing API calls with Django.
Observe the use of op_name in the example code blocks.
Compare with the content in the [testing.rst](https://github.com/graphql-python/graphene-django/blob/main/docs/testing.rst) file in the docs folder of the Graphene-Django GitHub repository, where operation_name is correctly used.
Expected Behavior
The online documentation should reflect the same parameter name, operation_name, as found in the GitHub repository documentation, ensuring consistency and correctness for developers relying on these docs for implementing tests.

Motivation / Use Case for Changing the Behavior
Ensuring the documentation is accurate and consistent across all platforms is crucial for developer experience and adoption. Incorrect documentation can lead to confusion and errors in implementation, especially for new users of Graphene-Django.