Fix warnings from nullabilty

PortableExecutable/VarData.cs

@@ -26,7 +26,11 @@
         /// <summary>
         /// The Unicode string L"Translation".
         /// </summary>
+#if NET48
         public string Key;
+#else
+        public string? Key;
+#endif
 
         /// <summary>
         /// As many zero words as necessary to align the Value member on a 32-bit boundary.
@@ -45,6 +49,10 @@
         /// independent. If the Var structure is omitted, the file will be interpreted as both
         /// language and code page independent.
         /// </summary>
+#if NET48
         public uint[] Value;
+#else
+        public uint[]? Value;
+#endif
     }
 }