Ignore SystemCallError in case it is raised by SSLSocket#accept.

Errno::ECONNRESET was raised by test_tls_post_connection_check and
test_tls_unknown_ca on mswin64 CI.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56923 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/net/ftp/test_ftp.rb

@@ -2230,7 +2230,7 @@ EOF
           sock.print("200 PSBZ success.\r\n")
           commands.push(sock.gets)
           sock.print("200 PROT success.\r\n")
-        rescue OpenSSL::SSL::SSLError
+        rescue OpenSSL::SSL::SSLError, SystemCallError
         end
       ensure
         sock.close