chore(cloudfront): fix example formatting in README (#30133)

Fix code formatting in README to make examples readable

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packages/aws-cdk-lib/aws-cloudfront/README.md

@@ -539,7 +539,7 @@ Additionally, you can load the function's code from a file using the `FunctionCo
 
 If you set `autoPublish` to false, the function will not be automatically published to the LIVE stage when it’s created.
 
-``ts
+```ts
 new cloudfront.Function(this, 'Function', {
   code: cloudfront.FunctionCode.fromInline('function handler(event) { return event.request }'),
   runtime: cloudfront.FunctionRuntime.JS_2_0,