build: use package-manager input for the screenshot workflow BM-1398 (#433)

### Motivation

Some [recent changes] to the **action-typescript** repository are
causing the [screenshot job] to fail.

[recent changes]:
https://github.com/linz/action-typescript/commits/master/?since=2025-10-07&until=2025-10-07
[screenshot job]:
https://github.com/linz/basemaps-screenshot/actions/runs/18330023138/job/52312482441

This repository uses [yarn] as a package manager. However, it does not
use the `package-manager` [workflow parameter provided by
action-typescript] to indicate this. We suspect that adding that
parameter will resolve the failure.

[yarn]: https://yarnpkg.com/
[workflow parameter provided by action-typescript]:
https://github.com/linz/action-typescript/blob/47be81e60ed1d891c696c3fb7f558876ba9a2b57/.github/workflows/main.yml#L6

### Modifications

- **workflows/`screenshot.yml`**

  - Added the `package-manager` input with a value of `yarn`.

### Verification

- The [screenshot job] is proceeding without issue again.

[screenshot job]:
https://github.com/linz/basemaps-screenshot/actions/runs/18390108503/job/52398202996?pr=433#step:2:162

Author: tawera-manaena

.github/workflows/screenshot.yml

@@ -15,6 +15,8 @@ jobs:
       contents: read
     steps:
       - uses: linz/action-typescript@v3
+        with:
+          package-manager: yarn
 
       - name: (Screenshot) Screenshot Pull Request Changes
         run: |