fix(tests): Clean up auth.allow-registration in system options tests

[joshuarli]

found in this shuffle-tests-across-shards run https://github.com/getsentry/sentry/actions/runs/22010195505/job/63602406261

this consistently fails:

pytest tests/sentry/api/endpoints/test_system_options.py::SystemOptionsTest::test_put_self_hosted_superuser_access_allowed tests/sentry/web/frontend/test_oauth_authorize.py::OAuthAuthorizeCustomSchemeTest::test_code_flow_unauthenticated_custom_scheme

and was bisected here https://github.com/getsentry/sentry/actions/runs/22013373357/job/63611146322

---

• Fix test pollution where SystemOptionsTest tests set auth.allow-registration to 1 via the API without cleaning up afterward
• The leaked option caused has_user_registration() to return True in subsequent tests, breaking login redirect behavior (returning 200 instead of 302) in OAuthAuthorizeCustomSchemeTest::test_code_flow_unauthenticated_custom_scheme
• Added options.delete("auth.allow-registration") cleanup in three tests: test_put_self_hosted_superuser_access_allowed, test_put_int_for_boolean, and test_update_channel

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Cleanup skipped if preceding assertion fails in test

Medium Severity

In test_update_channel, options.delete("auth.allow-registration") is placed after the get_last_update_channel assertion (lines 117–120). If that assertion fails, the cleanup never executes and the test pollution this PR aims to fix still occurs. In contrast, the other two tests (test_put_self_hosted_superuser_access_allowed, test_put_int_for_boolean) correctly place options.delete immediately after the PUT, before any assertions. Additionally, moving assert response.status_code == 200 to the very end means a failed PUT would produce a confusing error from the get_last_update_channel check instead of a clear status code failure.