Update Slovak language (#13187)

Marlin/src/lcd/language/language_en.h

 #ifndef MSG_SERVICE_RESET
   #define MSG_SERVICE_RESET                   _UxGT("Reset")
 #endif
+#ifndef MSG_SERVICE_IN
+  #define MSG_SERVICE_IN                      _UxGT(" in:")
+#endif

Marlin/src/lcd/language/language_sk.h

 #define MSG_TMC_HOMING_THRS                 _UxGT("Bezsenzor. domov")
 #define MSG_TMC_STEPPING_MODE               _UxGT("Režim krokovania")
 #define MSG_TMC_STEALTH_ENABLED             _UxGT("StealthChop zapnutý")
+
+#define MSG_SERVICE_RESET                   _UxGT("Vynulovať")
+#define MSG_SERVICE_IN                      _UxGT(" za:")

Marlin/src/lcd/menu/menu_info.cpp

     #if SERVICE_INTERVAL_1 > 0
       elapsed = stats.nextService1;
       elapsed.toString(buffer);
-      STATIC_ITEM(SERVICE_NAME_1 " in:", false, false);                                            // Service X in:
+      STATIC_ITEM(SERVICE_NAME_1 MSG_SERVICE_IN, false, false);                                    // Service X in:
       STATIC_ITEM("> ", false, false, buffer);                                                     // > 7d 12h 11m 10s
     #endif
     #if SERVICE_INTERVAL_2 > 0
       elapsed = stats.nextService2;
       elapsed.toString(buffer);
-      STATIC_ITEM(SERVICE_NAME_2 " in:", false, false);
+      STATIC_ITEM(SERVICE_NAME_2 MSG_SERVICE_IN, false, false);
       STATIC_ITEM("> ", false, false, buffer);
     #endif
     #if SERVICE_INTERVAL_3 > 0
       elapsed = stats.nextService3;
       elapsed.toString(buffer);
-      STATIC_ITEM(SERVICE_NAME_3 " in:", false, false);
+      STATIC_ITEM(SERVICE_NAME_3 MSG_SERVICE_IN, false, false);
       STATIC_ITEM("> ", false, false, buffer);
     #endif