Update Italian language, fix unused var warning (#13164)

Marlin/src/Marlin.cpp

       ExtUI::onFilamentRunout(ExtUI::getActiveTool());
     #endif
 
-    const char tool = '0'
-      #if NUM_RUNOUT_SENSORS > 1
-        + active_extruder
-      #endif
-    ;
+    #if ENABLED(HOST_PROMPT_SUPPORT) || ENABLED(HOST_ACTION_COMMANDS)
+      const char tool = '0'
+        #if NUM_RUNOUT_SENSORS > 1
+          + active_extruder
+        #endif
+      ;
+    #endif
 
     //action:out_of_filament
     #if ENABLED(HOST_PROMPT_SUPPORT)

Marlin/src/lcd/language/language_it.h

 #define MSG_GRADIENT                        _UxGT("Gradiente")
 #define MSG_FULL_GRADIENT                   _UxGT("Gradiente pieno")
 #define MSG_TOGGLE_MIX                      _UxGT("Alterna miscela")
-//#define MSG_CYCLE_MIX                       _UxGT("Ciclo miscela")
+#define MSG_CYCLE_MIX                       _UxGT("Ciclo miscela")
 #define MSG_GRADIENT_MIX                    _UxGT("Miscela gradiente")
 #define MSG_REVERSE_GRADIENT                _UxGT("Inverti gradiente")
 #define MSG_ACTIVE_VTOOL                    _UxGT("V-tool attivo")
-//#define MSG_START_VTOOL                     _UxGT("V-tool inizio")
-//#define MSG_END_VTOOL                       _UxGT("V-tool fine")
+#define MSG_START_VTOOL                     _UxGT("V-tool iniziale")
+#define MSG_END_VTOOL                       _UxGT("V-tool finale")
 #define MSG_GRADIENT_ALIAS                  _UxGT("V-tool alias")
 #define MSG_RESET_VTOOLS                    _UxGT("Ripristina V-tools")
 #define MSG_COMMIT_VTOOL                    _UxGT("Commit mix V-tool")