[mruby] Fix alignment of custom allocator for word boxing

src/VitalRouter.Unity/Assets/VitalRouter.MRuby/Runtime/MRubyContext.cs

@@ -75,7 +75,7 @@ static void Free(void* ptr)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         static void* Malloc(uint size)
         {
-            var allocated = UnsafeUtility.Malloc(size + HeaderSize, sizeof(byte), DefaultAllocator);
+            var allocated = UnsafeUtility.Malloc(size + HeaderSize, 4, DefaultAllocator);
             WriteHeader(allocated, size);
             return (byte*)allocated + HeaderSize;
         }