xUnit1051: HTTP helpers (GetAsync, PostAsJsonAsync, PutAsJsonAsync,
DeleteAsync) accept a CancellationToken that the test runner can use
to cancel a long-running suite. Forwarding TestContext.Current.
CancellationToken to every call lets the runner respond to Ctrl+C /
--blame-hang-timeout at the granularity of a single test instead of
the whole process.
Covers PublishEndpointTests (10 calls), CircleMembersApiTests
(11 calls) and BlogApiMappedClaimsTests (9 calls). BlogApiTests.cs
was already clean after 1868ed86.
