Flaky admin tests

[jsoref]

Failed jobs:

• ❌ https://github.com/check-spelling-sandbox/dart-lang-pub-dev/actions/runs/9210537288/job/25337876042

  ❌ test/publisher_test.dart: publisher publisher script (failed)
  Running dart pub publish --force in /tmp/pub-integrationEJHMGL/ORUHQF...
  Running dart pub publish --force in /tmp/pub-integrationEJHMGL/DYGUFH...
  TimeoutException: waiting for selector "#-admin-set-publisher-input" failed: timeout 5000ms exceeded
  
  Server processes completed.

• ❌ https://github.com/check-spelling-sandbox/dart-lang-pub-dev/actions/runs/9210537288/job/25337875040

  ❌ test/pkg_admin_page_test.dart: package admin page bulk tests (failed)
  Expected: 'check-spelling-sandbox/dart-lang-pub-dev'
    Actual: ''
     Which: is different. Both strings start the same, but the actual value is missing the following trailing characters: check-spel ...
  
  package:matcher                                                    expect
  test/pkg_admin_page_test.dart 69:11                                main.<fn>.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:pub_integration/src/fake_test_context_provider.dart 88:18  TestContextProvider.createTestUser.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:pub_integration/src/test_browser.dart 251:17               TestBrowserSession.withPage
  ===== asynchronous gap ===========================
  package:pub_integration/src/fake_test_context_provider.dart 87:[16](https://github.com/check-spelling-sandbox/dart-lang-pub-dev/actions/runs/9210537288/job/25337875040#step:6:18)  TestContextProvider.createTestUser.<fn>
  ===== asynchronous gap ===========================
  test/pkg_admin_page_test.dart 53:9                                 main.<fn>.<fn>
  Server processes completed.

Passing reruns:

• ✅ https://github.com/check-spelling-sandbox/dart-lang-pub-dev/actions/runs/9210537288/job/25339943349
• ✅ https://github.com/check-spelling-sandbox/dart-lang-pub-dev/actions/runs/9210537288/job/25339942402

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otherwise, CI in my forks is perfectly happy. (this is good, because I'm finalizing a patch series...)