Reduce sleep time in force-checkpointing-invoke test

- Change from 20s to 15s sleep to prevent cloud timeout
- Test was still timing out at 30s due to cloud environment overhead
- 15s + overhead should complete within 30s timeout

Author: ParidelPooya

packages/aws-durable-execution-sdk-js-examples/src/examples/force-checkpointing/invoke/force-checkpointing-invoke.ts

@@ -22,7 +22,7 @@ export const handler = withDurableExecution(
         return await branchCtx.step(
           "long-running-step",
           async () => {
-            await new Promise((resolve) => setTimeout(resolve, 20000));
+            await new Promise((resolve) => setTimeout(resolve, 15000));
             return "long-complete";
           },
           { retryStrategy: retryPresets.noRetry },