Use Test::Unit::PendedError instead of MiniTest::Skip for test-unit migration

(cherry picked from commit ruby/ruby@ecfbf1d)

Author: hsbt

test/openssl/utils.rb

@@ -294,8 +294,7 @@ def start_server(verify_mode: OpenSSL::SSL::VERIFY_NONE, start_immediately: true
             timeout = EnvUtil.apply_timeout_scale(30)
             th.join(timeout) or
               th.raise(RuntimeError, "[start_server] thread did not exit in #{timeout} secs")
-          rescue (defined?(MiniTest::Skip) ? MiniTest::Skip : Test::Unit::PendedError)
-            # MiniTest::Skip is for the Ruby tree
+          rescue Test::Unit::PendedError
             pend = $!
           rescue Exception
           end