[Bug]: Vertex AI Workbench access method in CloudSkillBoost lab

### File Name

Cloud SkillBoost Lab : https://partner.skills.google/course_templates/1322/labs/630731

### What happened?

A bug happened!

Link : (https://partner.skills.google/course_templates/1322)
Cloud SkillBoost Course: Implement RAG with Agent Platform
Lab : Improving RAG Solutions

**Steps to reproduce bug:**

Below is lab content asking lab taker to navigate to Google Cloud project by entering "Vertex AI Workbench" as per below instruction:
"In your Google Cloud project, navigate to Vertex AI Workbench. In the top search bar of the Google Cloud console, enter Vertex AI Workbench, and click on the first result."

However, Vertex AI Workbench is not available using this way. I have checked in the lab project, as well as existing GCP sandbox, to ensure this is not a specific lab environment creation issue, as shown below.

Lab screenshot:

Existing GCP project screenshot:

**Proposed Fix is as below:**

Navigate to Agent Platform -> Notebooks -> Workbench.

On clicking workbench, "generative-ai-jupyterlab" instance is available and accessible for use.

Am happy to submit PR for updating lab to fix this issue. I have researched and not found the GitHub code source repository yet so far. Any pointers are appreciated.

Thanks,
Srabasti Banerjee

### Relevant log output

```shell

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### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start with the Cloud SkillBoost lab at the linked course template and compare its Vertex AI Workbench instruction with the current Google Cloud console path. Locate the lab content source, update the navigation to Agent Platform → Notebooks → Workbench, and confirm that the generative-ai-jupyterlab instance is reachable as described.

Written by the indexing model from the issue text.