SetCookies_Success test is failing deterministically in CI

[ViktorHofer]

Example build: https://dev.azure.com/dnceng/public/_build/results?buildId=1178604

  Discovering: System.Net.Primitives.UnitTests.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Net.Primitives.UnitTests.Tests (found 36 test cases)
  Starting:    System.Net.Primitives.UnitTests.Tests (parallel test collections = on, max threads = 2)
    System.Net.Primitives.Unit.Tests.CookieContainerTest.SetCookies_Success(uri: http://uri.com/, cookieHeader: "name98=value98; path=/; domain=.uri.com; expires=W"..., expected: [name99=value99, name98=value98]) [FAIL]
      Assert.Equal() Failure
      Expected: 2
      Actual:   1
      Stack Trace:
        /_/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs(783,0): at System.Net.Primitives.Unit.Tests.CookieContainerTest.VerifyGetCookies(CookieContainer cc1, Uri uri, Cookie[] expected)
        /_/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs(376,0): at System.Net.Primitives.Unit.Tests.CookieContainerTest.SetCookies_Success(Uri uri, String cookieHeader, Cookie[] expected)
  Finished:    System.Net.Primitives.UnitTests.Tests
=== TEST EXECUTION SUMMARY ===
   System.Net.Primitives.UnitTests.Tests  Total: 151, Errors: 0, Failed: 1, Skipped: 0, Time: 4.457s

Will disable the test to unblock CI.

cc @dotnet/ncl

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Issue Details

---

Example build: https://dev.azure.com/dnceng/public/_build/results?buildId=1178604

  Discovering: System.Net.Primitives.UnitTests.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Net.Primitives.UnitTests.Tests (found 36 test cases)
  Starting:    System.Net.Primitives.UnitTests.Tests (parallel test collections = on, max threads = 2)
    System.Net.Primitives.Unit.Tests.CookieContainerTest.SetCookies_Success(uri: http://uri.com/, cookieHeader: "name98=value98; path=/; domain=.uri.com; expires=W"..., expected: [name99=value99, name98=value98]) [FAIL]
      Assert.Equal() Failure
      Expected: 2
      Actual:   1
      Stack Trace:
        /_/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs(783,0): at System.Net.Primitives.Unit.Tests.CookieContainerTest.VerifyGetCookies(CookieContainer cc1, Uri uri, Cookie[] expected)
        /_/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs(376,0): at System.Net.Primitives.Unit.Tests.CookieContainerTest.SetCookies_Success(Uri uri, String cookieHeader, Cookie[] expected)
  Finished:    System.Net.Primitives.UnitTests.Tests
=== TEST EXECUTION SUMMARY ===
   System.Net.Primitives.UnitTests.Tests  Total: 151, Errors: 0, Failed: 1, Skipped: 0, Time: 4.457s

Will disable the test to unblock CI.

cc @dotnet/ncl

Author:	ViktorHofer
Assignees:	-
Labels:	area-System.Net
Milestone:	-