Cache docs incompletely characterize when culling happens

[Jacob Walls]

See ​forum post: the cache docs incompletely describe how expired entries are culled:

Instead, expired cache entries are culled each time add(), set(), or touch() is called.

"Each time" neglects the role of MAX_ENTRIES here. (You have to exceed MAX_ENTRIES before any culling is done.)

[Sarah Boyce]

Thank you!
For others, I believe this area of the docs is being discussed: ​https://docs.djangoproject.com/en/6.0/topics/cache/#database-caching:~:text=Unlike,called

[Jacob Walls <jacobtylerwalls@…>]

In 1d71448:

Fixed #37129 -- Clarified database cache culling behavior in docs.

[Jacob Walls <jacobtylerwalls@…>]

In d45fc0a:

[6.1.x] Fixed #37129 -- Clarified database cache culling behavior in docs.

Backport of 1d714484f67777e586fbea49ec743a7e39cba50f from main.