Remove a pend that hides missing support for SSL_CTX_set_client_cert_cb()
in the TLSv1.3 stack.

Index: test/openssl/test_ssl.rb
--- test/openssl/test_ssl.rb.orig
+++ test/openssl/test_ssl.rb
@@ -479,7 +479,9 @@ class OpenSSL::TestSSL < OpenSSL::SSLTestCase
   end
 
   def test_client_ca
-    pend "LibreSSL doesn't support certificate_authorities" if libressl?
+    if ENV['SKIP_EXPECTED_FAILURES']
+      pend "skip failing client CA test"
+    end
 
     ctx_proc = Proc.new do |ctx|
       store = OpenSSL::X509::Store.new
