Fixed redefinition warnings of MSG_HOTEND_TOO_COLD. (#12203)

Marlin/src/core/language.h

 #define MSG_ENDSTOPS_HIT                    "endstops hit: "
 #define MSG_ERR_COLD_EXTRUDE_STOP           " cold extrusion prevented"
 #define MSG_ERR_LONG_EXTRUDE_STOP           " too long extrusion prevented"
-#define MSG_HOTEND_TOO_COLD                 "Hotend too cold"
+#define MSG_ERR_HOTEND_TOO_COLD             "Hotend too cold"
 
 #define MSG_FILAMENT_CHANGE_HEAT            "Press button (or M108) to heat nozzle"
 #define MSG_FILAMENT_CHANGE_INSERT          "Insert filament and press button (or M108)"

Marlin/src/feature/pause.cpp

   #if ENABLED(PREVENT_COLD_EXTRUSION)
     if (!DEBUGGING(DRYRUN) && thermalManager.targetTooColdToExtrude(active_extruder)) {
       SERIAL_ERROR_START();
-      SERIAL_ERRORLNPGM(MSG_HOTEND_TOO_COLD);
+      SERIAL_ERRORLNPGM(MSG_ERR_HOTEND_TOO_COLD);
       return false;
     }
   #endif
 
   if (!DEBUGGING(DRYRUN) && unload_length && thermalManager.targetTooColdToExtrude(active_extruder)) {
     SERIAL_ERROR_START();
-    SERIAL_ERRORLNPGM(MSG_HOTEND_TOO_COLD);
+    SERIAL_ERRORLNPGM(MSG_ERR_HOTEND_TOO_COLD);
 
     #if ENABLED(ULTIPANEL)
       if (show_lcd) { // Show status screen

Marlin/src/module/tool_change.cpp

         #if ENABLED(PREVENT_COLD_EXTRUSION)
           if (!DEBUGGING(DRYRUN) && thermalManager.targetTooColdToExtrude(active_extruder) && toolchange_settings.swap_length) {
             SERIAL_ERROR_START();
-            SERIAL_ERRORLNPGM(MSG_HOTEND_TOO_COLD);
+            SERIAL_ERRORLNPGM(MSG_ERR_HOTEND_TOO_COLD);
             active_extruder = tmp_extruder;
             return;
           }