📌 Creality RAMPS optional SD_DETECT_PIN (#23740)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/pins/ramps/pins_RAMPS_CREALITY.h

 #endif
 
 #ifndef SD_DETECT_PIN
-  #define SD_DETECT_PIN                       49  // Always define onboard SD detect
+  #if SD_CONNECTION_IS(ONBOARD)
+    //#define HAS_ONBOARD_SD_DETECT               // If the SD_DETECT_PIN is wired up
+  #endif
+  #if ENABLED(HAS_ONBOARD_SD_DETECT) || !SD_CONNECTION_IS(ONBOARD)
+    #define SD_DETECT_PIN                     49
+  #endif
 #endif
 
 #ifndef PS_ON_PIN