Update django-countries requirement from ==7.6.* to ==8.2.* (#5660)

* Update django-countries requirement from ==7.6.* to ==8.2.*

Updates the requirements on [django-countries](https://github.com/SmileyChris/django-countries) to permit the latest version.
- [Changelog](https://github.com/SmileyChris/django-countries/blob/main/CHANGES.md)
- [Commits](https://github.com/SmileyChris/django-countries/compare/v7.6...v8.2.0)

---
updated-dependencies:
- dependency-name: django-countries
  dependency-version: 8.2.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* Update our helpers

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Raphael Michel <michel@rami.io>

src/pretix/helpers/countries.py

@@ -40,6 +40,10 @@ class CachedCountries(Countries):
         django-countries performs a unicode-aware sorting based on pyuca which is incredibly
         slow.
         """
+        # Starting in django-countries 8.1, django-countries implemented a similar caching, but only on object level.
+        # We keep our caching for now for the added caching to the cache store. Unfortunately we can't really avoid
+        # the double-caching on object level if we want the caches od be used in a sensible order. We could re-evaluate
+        # and drop this in the future if it ever causes bugs or memory issues.
         cache_key = "countries:all:{}".format(get_language_without_region())
         if self.cache_subkey:
             cache_key += ":" + self.cache_subkey
@@ -84,8 +88,6 @@ class FastCountryField(CountryField):
             *self._check_backend_specific_checks(**kwargs),
             *self._check_validators(),
             *self._check_deprecation_details(),
-            *self._check_multiple(),
-            *self._check_max_length_attribute(**kwargs),
         ]