Sanity-check mutually-exclusive G34 features (#19706)

Marlin/src/inc/SanityCheck.h

   #endif
 #endif
 
+#if BOTH(Z_STEPPER_AUTO_ALIGN, MECHANICAL_GANTRY_CALIBRATION)
+  #error "You cannot use Z_STEPPER_AUTO_ALIGN and MECHANICAL_GANTRY_CALIBRATION at the same time."
+#endif
+
 #if ENABLED(PRINTCOUNTER) && DISABLED(EEPROM_SETTINGS)
   #error "PRINTCOUNTER requires EEPROM_SETTINGS. Please update your Configuration."
 #endif