problem using html_minify in django

Hi, thank you for doing this project!

I am trying to manually minify a view in a django project, but I don't have it integrated to the middleware (other views are already taken care of and have a build process)
But I expected to be able to call html_minify on the output of a call to django.shortcuts.render.
Instead I get:
```
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/django/core/handlers/exception.py", line 34, in inner
response = get_response(request)
File "/usr/local/lib/python3.8/site-packages/debug_toolbar/middleware.py", line 67, in __call__
panel.generate_stats(request, response)
File "/usr/local/lib/python3.8/site-packages/debug_toolbar/panels/headers.py", line 53, in generate_stats
self.response_headers = OrderedDict(sorted(response.items()))

Exception Type: AttributeError at /v/27/
Exception Value: 'str' object has no attribute 'items'
```
Maybe there is something in newer django? Or is there some intermediate step in this possibly unusal workflow?

Start by tracing how html_minify is called on the result of django.shortcuts.render and compare that workflow with the middleware path shown in the traceback. Reproduce the AttributeError involving django-debug-toolbar, then determine whether the manual-render workflow needs a code change or clearer usage guidance.

Written by the indexing model from the issue text.