fix: correct nullability spelling in exception (#89)

Author: inputfalken

src/DynamoDBGenerator.SourceGenerator/Types/TypeIdentifier.cs

@@ -24,7 +24,7 @@ protected TypeIdentifier(ITypeSymbol typeSymbol)
             { IsValueType: true, OriginalDefinition.SpecialType: SpecialType.System_Nullable_T } => true,
             { IsValueType: true } => false,
             _ => throw new ArgumentOutOfRangeException(
-                $"Could not determine nullablity of type '{typeSymbol.ToDisplayString()}'.")
+                $"Could not determine nullability of type '{typeSymbol.ToDisplayString()}'.")
         };
 
         TypeSymbol = typeSymbol;