Verify that the PATH has been set up correctly

When creating copies with yabridgectl. This should at least give an
advance warning that some additional steps are required when first
setting up yabridge.

src/plugin/plugin-bridge.cpp

@@ -422,7 +422,7 @@ intptr_t PluginBridge::dispatch(AEffect* /*plugin*/,
         logger.log_event(true, opcode, index, value, nullptr, option,
                          std::nullopt);
         logger.log(
-            "   WARNING: The host has dispatched an event before the plugin "
+            "   Warning: The host has dispatched an event before the plugin "
             "has finished initializing, ignoring the event. (are we running "
             "Ardour 5.X?)");
         logger.log_event_response(true, opcode, 0, nullptr, std::nullopt);