Deprecation warning for action_location parameter should mention subclass and/or point to user code

[Jacob Walls]

As pointed out in #37187, we have deprecation warnings being emitted on wsgiref frames for the deprecation warning added in #12090:

/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/wsgiref/handlers.py:137: RemovedInDjango70Warning: Overriding get_action_choices() without the 'action_location' parameter is deprecated. Update the signature to get_action_choices(self, request, default_choices=None, action_location=ActionLocation.CHANGE_LIST).

Analysis from #37187:

... trying to warn about an overridden subclass method that has already been called so is no longer on the stack.

[Mike Edmunds]

The new warnings.warn_explicit() helper being proposed for #37187 could also cover this.

[Mike Edmunds]

​https://github.com/django/django/pull/21553

[Jacob Walls <jacobtylerwalls@…>]

In 2e48636c:

Fixed #37187, #37190 -- Pointed ModelAdmin warnings to the deprecated code.

Used warn_about_implementation() for ModelAdmin deprecation warnings on
get_list_select_related() return value and missing action_location
parameters in get_actions() and get_action_choices(). Fixes a problem
where the warnings would point to wsgiref rather than the ModelAdmin
subclass using deprecated functionality.

[Jacob Walls <jacobtylerwalls@…>]

In bc529fb8:

[6.1.x] Fixed #37187, #37190 -- Pointed ModelAdmin warnings to the deprecated code.

Used warn_about_implementation() for ModelAdmin deprecation warnings on
get_list_select_related() return value and missing action_location
parameters in get_actions() and get_action_choices(). Fixes a problem
where the warnings would point to wsgiref rather than the ModelAdmin
subclass using deprecated functionality.

Backport of 2e48636c54910e435eb31e1b7d8a8089c84233ad from main.