Use public API to update Setting values
In #30354 we've fixed this in tests, but we are updating setting directly in database in http_proxy callback, we should not do so :)
Fixes #32285 - use public API to update setting
We are updating setting for content proxy directly in database, but that
blocks efforts in core to migrate all settings into memory.
This would just break tests, as in production settings will be loaded
from database per request anyway, but it is still better to access
Setting through public API.