🎨 Call millis() once in manage_inactivity (#22363)

Marlin/src/MarlinCore.cpp

@@ -510,7 +510,6 @@ inline void manage_inactivity(const bool no_stepper_sleep=false) {
     constexpr millis_t HOME_DEBOUNCE_DELAY = 1000UL;
     static millis_t next_home_key_ms; // = 0
     if (!IS_SD_PRINTING() && !READ(HOME_PIN)) { // HOME_PIN goes LOW when pressed
-      const millis_t ms = millis();
       if (ELAPSED(ms, next_home_key_ms)) {
         next_home_key_ms = ms + HOME_DEBOUNCE_DELAY;
         LCD_MESSAGEPGM(MSG_AUTO_HOME);
@@ -522,7 +521,6 @@ inline void manage_inactivity(const bool no_stepper_sleep=false) {
   #if ENABLED(CUSTOM_USER_BUTTONS)
     // Handle a custom user button if defined
     const bool printer_not_busy = !printingIsActive();
-    const millis_t ms = millis();
     #define HAS_CUSTOM_USER_BUTTON(N) (PIN_EXISTS(BUTTON##N) && defined(BUTTON##N##_HIT_STATE) && defined(BUTTON##N##_GCODE))
     #define HAS_BETTER_USER_BUTTON(N) HAS_CUSTOM_USER_BUTTON(N) && defined(BUTTON##N##_DESC)
     #define _CHECK_CUSTOM_USER_BUTTON(N, CODE) do{                     \