Fix CA1308 warning in LINQ expression processing

- Add pragma directive to suppress CA1308 warning with proper rationale
- Bing API specifically expects lowercase boolean values (true/false)
- ToLowerInvariant() is the correct choice for this API compatibility requirement
- All builds now clean with 0 warnings, tests continue to pass (48/48)

Author: alzarei

dotnet/src/Plugins/Plugins.Web/Bing/BingTextSearch.cs

@@ -227,7 +227,10 @@ private static void ProcessEqualityExpression(BinaryExpression binaryExpr, TextS
             if (bingFilterName != null && value != null)
             {
                 // Convert boolean values to lowercase strings for Bing API compatibility
+                // CA1308: Using ToLowerInvariant() is intentional here as Bing API expects boolean values in lowercase format (true/false)
+#pragma warning disable CA1308 // Normalize strings to uppercase
                 string stringValue = value is bool boolValue ? boolValue.ToString().ToLowerInvariant() : value.ToString() ?? string.Empty;
+#pragma warning restore CA1308 // Normalize strings to uppercase
 
                 if (isNegated)
                 {