Add closedDate to trimmed pull request data (Issue #709) (#733)

Add closedDate to trimmed pull request data

## GitHub issue number
Fixes #709 

## **Associated Risks**
None

## ✅ **PR Checklist**

- [x] **I have read the [contribution
guidelines](https://github.com/microsoft/azure-devops-mcp/blob/main/CONTRIBUTING.md)**
- [x] **I have read the [code of conduct
guidelines](https://github.com/microsoft/azure-devops-mcp/blob/main/CODE_OF_CONDUCT.md)**
- [x] Title of the pull request is clear and informative.
- [x] 👌 Code hygiene
- [x] 🔭 Telemetry added, updated, or N/A
- [x] 📄 Documentation added, updated, or N/A
- [x] 🛡️ Automated tests added, or N/A

## 🧪 **How did you test it?**

Manually tested

Author: nikolapeja6

src/tools/repositories.ts

@@ -124,6 +124,7 @@ function trimPullRequest(pr: GitPullRequest, includeDescription = false) {
       uniqueName: pr.createdBy?.uniqueName,
     },
     creationDate: pr.creationDate,
+    closedDate: pr.closedDate,
     title: pr.title,
     ...(includeDescription ? { description: pr.description ?? "" } : {}),
     isDraft: pr.isDraft,