retry connection to avoid fragile tests

```
Error: test_next_goes_to_the_next_statement(DEBUGGER__::NextTest): Errno::ECONNREFUSED: Connection refused - connect(2) for 127.0.0.1:44075
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:64:in `connect'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:64:in `connect_internal'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:137:in `connect'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:641:in `block in tcp'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:227:in `each'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:227:in `foreach'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/socket.rb:631:in `tcp'
/home/runner/work/debug/debug/test/support/protocol_test_case.rb:402:in `attach_to_cdp_server'
/home/runner/work/debug/debug/test/support/protocol_test_case.rb:320:in `execute_cdp_scenario'
/home/runner/work/debug/debug/test/support/protocol_test_case.rb:47:in `block in run_protocol_scenario'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/timeout.rb:93:in `block in timeout'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/timeout.rb:33:in `block in catch'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/timeout.rb:33:in `catch'
/opt/hostedtoolcache/Ruby/2.6.10/x64/lib/ruby/2.6.0/timeout.rb:108:in `timeout'
/home/runner/work/debug/debug/test/support/protocol_test_case.rb:44:in `run_protocol_scenario'
/home/runner/work/debug/debug/test/protocol/next_test.rb:20:in `test_next_goes_to_the_next_statement'
```

Author: ko1

test/support/protocol_test_case.rb

@@ -399,7 +399,16 @@ def attach_to_cdp_server
         sleep 0.001 until @remote_info.debuggee_backlog.join.include? 'Disconnected.'
       end
 
-      sock = Socket.tcp HOST, @remote_info.port
+      retry_cnt = 0
+      begin
+        sock = Socket.tcp HOST, @remote_info.port
+      rescue Errno::ECONNREFUSED
+        raise if (retry_cnt += 1) > 10 # retry up to 10 times
+
+        sleep 0.1
+        retry
+      end
+
       uuid = body[0][:id]
 
       Timeout.timeout(TIMEOUT_SEC) do