Update null-conditional-operator_1.cs (#3362)

Author: cirelli94

docs/csharp/language-reference/operators/codesnippet/CSharp/null-conditional-operator_1.cs

@@ -15,7 +15,7 @@ static void Main()
             int? x = null;
 
             // Set y to the value of x if x is NOT null; otherwise,
-            // if x = null, set y to -1.
+            // if x == null, set y to -1.
             int y = x ?? -1;
 
             // Assign i to return value of the method if the method's result
@@ -28,4 +28,4 @@ static void Main()
             // display the string "Unspecified".
             Console.WriteLine(s ?? "Unspecified");
         }
-    }
+    }