perf(tests): isolate network E2E and await QUIC cleanup

backend/tests/MoShiro.Backend.Tests/EnrollmentAndTaskSetTests.cs

@@ -376,7 +376,7 @@ public sealed class EnrollmentAndTaskSetTests : IClassFixture<BackendFixture>
         JsonNode listed = await _backend.GetJsonAsync(_backend.Admin, "/api/admin/probes");
         Assert.Contains(listed["items"]!.AsArray(), p => p!["id"]!.GetValue<string>() == id && !p["revoked"]!.GetValue<bool>());
         string duplicateToken = await _backend.CreateJoinTokenAsync(role: "probe");
-        using var http = new HttpClient();
+        using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(15) };
         Fleet.Core.Result<Fleet.Enrollment.Client.EnrollmentResult> duplicate = await Fleet.Enrollment.Client.EnrollmentClient.EnrollAsync(
             http, _backend.BaseAddress, duplicateToken, name, Path.Combine(Path.GetTempPath(), "moshiro-dup-" + Guid.NewGuid().ToString("N")), "0.0.0", null, TimeProvider.System, default);
         Assert.False(duplicate.IsSuccess);