Take into account serverless debug probes when configuring debug speed

Resolve platformio/platformio-core#3864

Author: valeros

platform.py

@@ -182,9 +182,9 @@ def _add_default_debug_tools(self, board):
 
     def configure_debug_options(self, initial_debug_options, ide_data):
         debug_options = copy.deepcopy(initial_debug_options)
-        server_executable = debug_options["server"]["executable"].lower()
         adapter_speed = initial_debug_options.get("speed")
         if adapter_speed:
+            server_executable = debug_options["server"].get("executable", "").lower()
             if "openocd" in server_executable:
                 debug_options["server"]["arguments"].extend(
                     ["-c", "adapter speed %s" % adapter_speed]