fix(lambda-runtime): change fallback for latest lambda node runtime to node 22.x (#35764)

### Reason for this change
For #34635, moving the fallback of latest lambda node runtime to node 22.x



### Description of changes

Changed fallback in `determineLatestNodeRuntime` to Nodejs 22.x for users that use AWS account in regions which don't have aregional fact present

### Description of how you validated changes
Ran all unit and integration tests to check that the change is valid

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: kumvprat

packages/@aws-cdk-testing/framework-integ/test/aws-apigateway/test/authorizers/integ.api-with-authorizer-and-proxy.js.snapshot/apigatewaywithauthorizerandproxyDefaultTestDeployAssertDBEA1774.assets.json

@@ -422,7 +422,7 @@
       "Arn"
      ]
     },
-    "Runtime": "nodejs18.x"
+    "Runtime": "nodejs20.x"
    },
    "DependsOn": [
     "lambdas3ServiceRoleC9EDE33A"

packages/@aws-cdk-testing/framework-integ/test/aws-apigateway/test/authorizers/integ.api-with-authorizer-and-proxy.js.snapshot/cdk.out

@@ -42,7 +42,7 @@ const sendResource = root.addResource('InitiateAction');
 const myfunc = new lambda.Function(stack, 'lambda-s3', {
   code: lambda.AssetCode.fromAsset(path.join(__dirname, 'assets')),
   handler: 'index.handler',
-  runtime: lambda.Runtime.NODEJS_18_X,
+  runtime: lambda.Runtime.NODEJS_20_X,
 });
 
 const sendLambdaIntegration = new agw.LambdaIntegration(myfunc);

packages/@aws-cdk-testing/framework-integ/test/aws-apigateway/test/authorizers/integ.api-with-authorizer-and-proxy.js.snapshot/integ.json

@@ -44,7 +44,7 @@
       "Arn"
      ]
     },
-    "Runtime": "nodejs18.x"
+    "Runtime": "nodejs20.x"
    },
    "DependsOn": [
     "myfnServiceRole7822DC24"