See #110016 for context.

• migrate dev/devicelab/test/runner_test.dart:5:// @dart = 2.8: Migrate device lab runner to null safety #110582

• [-] files excluded to test backwards compatibility with pre 2.12:

  dev/integration_tests/web/lib/null_assert_main.dart:5:// @dart = 2.8
  packages/flutter/test/foundation/_compute_caller_unsound_null_safety.dart:5:// @dart=2.9
  packages/flutter/test/foundation/_compute_caller_unsound_null_safety_error.dart:5:// @dart=2.9
  

• convert dev/integration_tests/android_semantics_testing to null safety (Migrate android_semantics_testing to null safety #90633)

• Remaining flutter/flutter work - flutter_tools - tracked in Migrate flutter CLI tool to null safety #71511)