Fix line highlighting in C#, Swift, and PHP retry code snippets

- Changed C# client-level highlight from {3} to {4}
- Changed Swift client-level highlight from {4} to {5}
- Changed PHP client-level highlight from {3} to {4}
- All highlights now correctly point to the maxRetries configuration line

Co-Authored-By: Niels Swimberghe <[email protected]>

Author: devin-ai-integration[bot]

fern/products/sdks/guides/retries-with-backoff.mdx

@@ -69,7 +69,7 @@ default retry limit when instantiating the client.
     ```
   </CodeBlock>
   <CodeBlock title="C#">
-    ```csharp {3}
+    ```csharp {4}
     using Imdb;
 
     var client = new ImdbClient(new ClientOptions {
@@ -78,7 +78,7 @@ default retry limit when instantiating the client.
     ```
   </CodeBlock>
   <CodeBlock title="Swift">
-    ```swift {4}
+    ```swift {5}
     import Imdb
 
     let client = ImdbClient(
@@ -88,7 +88,7 @@ default retry limit when instantiating the client.
     ```
   </CodeBlock>
   <CodeBlock title="PHP">
-    ```php {3}
+    ```php {4}
     use Imdb\ImdbClient;
 
     $client = new ImdbClient([