Fix for unicode-ignorant gcc preprocessor

Marlin/src/HAL/HAL_AVR/HAL_AVR.h

@@ -150,7 +150,7 @@ extern "C" {
 
 #define _CAT(a, ...) a ## __VA_ARGS__
 #define HAL_timer_set_compare(timer, compare) (_CAT(TIMER_OCR_, timer) = compare)
-#define HAL_timer_restrain(timer, interval_µs) NOLESS(_CAT(TIMER_OCR_, timer), _CAT(TIMER_COUNTER_, timer) + interval_µs * HAL_TICKS_PER_US)
+#define HAL_timer_restrain(timer, interval_us) NOLESS(_CAT(TIMER_OCR_, timer), _CAT(TIMER_COUNTER_, timer) + interval_us * HAL_TICKS_PER_US)
 
 #define HAL_timer_get_compare(timer) _CAT(TIMER_OCR_, timer)
 #define HAL_timer_get_count(timer) _CAT(TIMER_COUNTER_, timer)