Unquarantine HubConnectionTests.ServerWithOldProtocolVersionClientWithNewProtocolVersionWorksDoesNotAllowStatefulReconnect (#66886)

This test has been passing 100% in the quarantine pipeline for 30+ days
and is being unquarantined.

Closes #51361

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/SignalR/clients/csharp/Client/test/FunctionalTests/HubConnectionTests.cs

@@ -2843,7 +2843,6 @@ public async Task CanSetMessageBufferSizeOnClient()
     }
 
     [Fact]
-    [QuarantinedTest("https://github.com/dotnet/aspnetcore/issues/51361")]
     public async Task ServerWithOldProtocolVersionClientWithNewProtocolVersionWorksDoesNotAllowStatefulReconnect()
     {
         bool ExpectedErrors(WriteContext writeContext)