Update flake8 requirement from ==7.1.* to ==7.2.* (#4972)

* Update flake8 requirement from ==7.1.* to ==7.2.*

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Commits](https://github.com/pycqa/flake8/compare/7.1.0...7.2.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:production
...

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

* Resolve warning

---------

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/base/signals.py

@@ -46,7 +46,6 @@ app_cache = {}
 
 
 def _populate_app_cache():
-    global app_cache
     apps.check_apps_ready()
     for ac in apps.app_configs.values():
         app_cache[ac.name] = ac