Fix bad sanitycheck (#12748)

Marlin/src/inc/SanityCheck.h

@@ -1121,8 +1121,10 @@ static_assert(X_MAX_LENGTH >= X_BED_SIZE && Y_MAX_LENGTH >= Y_BED_SIZE,
 
 #endif
 
-#if HAS_MESH && DISABLED(JUNCTION_DEVIATION)
+#if HAS_MESH
+  #if DISABLED(JUNCTION_DEVIATION)
     static_assert(DEFAULT_ZJERK > 0.1, "Low DEFAULT_ZJERK values are incompatible with mesh-based leveling.");
+  #endif
 #elif ENABLED(G26_MESH_VALIDATION)
   #error "G26_MESH_VALIDATION requires MESH_BED_LEVELING, AUTO_BED_LEVELING_BILINEAR, or AUTO_BED_LEVELING_UBL."
 #endif