esp_event: add missing header include

Required header was indirectly getting resolved through lwip includes,
apparently does not work if application is not using lwip networking stack.

components/esp_event/default_event_loop.c

@@ -14,6 +14,7 @@
 
 #include "esp_event.h"
 #include "esp_event_internal.h"
+#include "esp_task.h"
 
 /* ------------------------- Static Variables ------------------------------- */