Flaky on windows-latest: OAuth metadata fetch times out in in-memory tests (same class as #1701, not covered by #1702)

GetAuthServerMetadataAsync を読み、#1702 で追加された server/discover プローブのタイムアウト処理と比較してください。3 つの名前付きテストから開始して、windows-latest の Build and Test レッグを再実行し、失敗を再現してください。メタデータ取得のタイムアウトがアサーション失敗ではなくタイムアウトエラーとして表面化し、影響を受けるテストが決定的になれば完了です。

Describe the bug

Several OAuth tests occasionally fail on the windows-latest legs of Build and Test.
If that occurs, the GetAuthServerMetadataAsync method gets a TaskCancelledException
during a slow TLS handshake using the in-memory duplex pipe, ClientOAuthProvider wraps
that into the "Failed to find .well-known/..." message, and assertion expectations
about that message fail on the injected text – that is, the error manifests itself as
a confusing assertion failure instead of a timeout.

It appears to be similar to #1701 from the OAuth side of things. #1702 increased
the server/discover probe timeout in the in-memory tests, but the OAuth metadata
path has a similar timeout which was not added and is still failing after that merge.

Tests affected so far:

• OAuth.AuthTests.CannotAuthenticate_WithInvalidClientMetadataDocument
• OAuth.DcrFailureTests.DcrRejection_PropagatesToConsumer_WithStatusBodyAndSentParameters
• ClientConformanceTests.RunConformanceTest(scenario: "auth/offline-access-scope")

To Reproduce
Intermittent, not deterministic reproduction possible. It is reproduced by running Build and Tests
of windows-latest leg multiple times.

The following two incidents are on August 9, right after merging PR #1702, for two consecutive
commits of the same branch which are identical but different in comments and tests:

1. a9f02522 - windows-latest, Debug - job - auth/offline-access-scope
2. e07f4999 - windows-latest, Release - [job](https://

Expected behavior
Tests need to be deterministic. In case the timeout happens during fetching of the metadata, the issue should be thrown as a timeout and not as an assertion failure on an error message that’s not related to it at all.

Logs
From the e07f4999 Release run