Extraneous and confusing ModelAdmin select_related deprecation warnings

[Mike Edmunds]

Some of the deprecation warnings introduced in 122f0b62a1effa558aad67a62e5b0d84a49cdc23 (as a follow-up to #36593):

• Are issued against Django internals or wsgiref/handlers.py (or whatever code is serving the admin site)—not against the code that is responsible for the deprecated behavior.
• Sometimes include an extra warning that "Calling select_related() with no arguments is deprecated," even though select_related() is not called anywhere in the user's code.

To reproduce (Django 6.1b1, run with PYTHONWARNINGS=always to see all deprecations):

1. Have a models.Author and models.Book with a foreign key to author.
2. Define admin.BookAdmin with a get_select_related() method that returns the deprecated value True:

   from django.contrib import admin
   from .models import Author, Book
   
   class BookAdmin(admin.ModelAdmin):
       list_display = ['title', 'author__name']
   
       def get_list_select_related(self, request):
           return True  # deprecated return value
   
   admin.site.register(Author)
   admin.site.register(Book, BookAdmin)
   

3. Run the devserver and visit /admin/yourapp/books/

Results: the warning about returning True from get_list_select_related() points to Django's internals, and there's an extra warning about wsgiref/handlers.py calling select_related() with no arguments:

.venv/lib/python3.14/site-packages/django/contrib/admin/options.py:930: RemovedInDjango70Warning: Returning True from ModelAdmin.get_list_select_related() is deprecated. Return False or a list or tuple of fields to fetch instead.
  warnings.warn(
.pyenv/versions/3.14.3/lib/python3.14/wsgiref/handlers.py:137: RemovedInDjango70Warning: Calling select_related() with no arguments is deprecated. Specify the fields to fetch instead.
  self.result = application(self.environ, self.start_response)

Expected: ideally, something that points to the BookAdmin implementation (and nothing about calling select_related()):

.../example-project/yourapp/admin.py:7: RemovedInDjango70Warning: Returning True from ModelAdmin.get_list_select_related() is deprecated. Return False or a list or tuple of fields to fetch instead.
  def get_list_select_related(self, request):

There are two issues here:

1. ModelAdmin.get_changelist_instance() is trying to warn about an overridden subclass method that has already been called so is no longer on the stack. (It's also missing skip_file_prefixes, which is why it's blaming Django internals. But adding that would just move the blame to wsgiref—still not helpful.)
2. QuerySet.select_related() is unconditionally issuing a deprecation warning, even when it's being used internally to implement a deprecated feature elsewhere in Django (like in ModelAdmin).

The second problem is easily solved: we implemented warn_about_external_use() specifically for this use case.

The first problem is probably solvable by using warnings.warn_explicit() to point to the subclass method that is actually at fault. (I'm looking into that now.) If that doesn't work, we could change the warning message to include the actual subclass name: Returning True from yourapp.admin.BookAdmin.get_list_select_related() is deprecated.

Also:

• If you replace BookAdmin.get_list_select_related() with list_select_related = True, you get a nice startup-time warning that points at the class BookAdmin definition in your own admin.py. But you still get the extraneous select_related() warning in wsgiref when visiting the view.
• If you load the admin view from a test, the warnings will point to the self.client.get("/admin/core/books/") line instead of wsgiref. (That at least gives you some idea which code might be the problem.)
• I suspect there's a similar issue with the warning for overriding get_actions()/get_action_choices() without the 'action_location' parameter (from #12090 - f30acb184f75fd9260cfd6ddc48a3bbbd49f9c1d).
• The extraneous select_related() warning occurs in Django's tests, but is being suppressed by #37072. (The PR for that issue made it visible, and pulling that thread lead to this.)