Disable failing test SignedXmlTest.VerifyXmlResolver (#76129)

PR #75369 tried to fix the problem and re-enabled the test, but it is still failing.
Tracked by #74115

src/libraries/System.Security.Cryptography.Xml/tests/SignedXmlTest.cs

@@ -1594,6 +1594,7 @@ public void VerifyHMAC_HMACOutputLength_Invalid()
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/74115")]
         public void VerifyXmlResolver(bool provideResolver)
         {
             TcpListener listener = new TcpListener(IPAddress.Loopback, 0);