Fix: define _TASK_THREAD_SAFE for TaskScheduler

the TaskScheduler runs in the context of a FreeRTOS thread/task. there
are other such threads (MQTT client and web server in particular). to
allow changing TaskScheduler task properties from different threads, we
need to enable the use of a mutex to protect the TaskScheduler.

platformio.ini

@@ -24,6 +24,7 @@ platform = espressif32@6.5.0
 build_flags =
     -DPIOENV=\"$PIOENV\"
     -D_TASK_STD_FUNCTION=1
+    -D_TASK_THREAD_SAFE=1
     -Wall -Wextra -Wunused -Wmisleading-indentation -Wduplicated-cond -Wlogical-op -Wnull-dereference
 ;   Have to remove -Werror because of
 ;   https://github.com/espressif/arduino-esp32/issues/9044 and