fix: escape && in XML doc comment (CS1570)

Author: wendellmva

src/lib/TinyTemplateEngine.cs

@@ -565,7 +565,7 @@ private bool EvaluateCondition(string condition, ExecutionContext context)
     }
 
     /// <summary>
-    /// Finds a logical operator (&&, ||) that's not inside parentheses.
+    /// Finds a logical operator (&amp;&amp;, ||) that's not inside parentheses.
     /// </summary>
     private static int FindOperatorOutsideParentheses(string condition, string op)
     {