Disable frequently failing GetAsync_SupportedSSLVersion_Succeeds test

Author: stephentoub

src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.SslProtocols.cs

@@ -147,6 +147,7 @@ public static IEnumerable<object[]> SupportedSSLVersionServers()
 
         // We have tests that validate with SslStream, but that's limited by what the current OS supports.
         // This tests provides additional validation against an external server.
+        [ActiveIssue(26186)]
         [OuterLoop("Avoid www.ssllabs.com dependency in innerloop.")]
         [Theory]
         [MemberData(nameof(SupportedSSLVersionServers))]