Add django 5.2 support

[scpaes]

This issue proposes updating the supported Django version for this project to Django 5.2, which is the latest Long Term Support (LTS) release. Currently, the project supports older Django versions, and aligning with the latest LTS release will ensure compatibility with modern Django applications and leverage new features and security improvements.

[spookylukey]

Is django-paypal broken under Django 5.2? If so, what is the specific issue?

[scpaes]

Is django-paypal broken under Django 5.2? If so, what is the specific issue?

My apologies; I should have provided more context. My goal is to contribute by either adding or confirming official support for Django 5.2. Currently, it's uncertain whether Django 5.2 is supported, according to both PyPI and the project's test matrix. I'd like to help make this official.