chore(deps): update pnpm/action-setup action to v6 (#129)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [pnpm/action-setup](https://github.com/pnpm/action-setup) | action | major | `v5` → `v6` |

---

### Release Notes

<details>
<summary>pnpm/action-setup (pnpm/action-setup)</summary>

### [`v6`](https://github.com/pnpm/action-setup/compare/v5...v6)

[Compare Source](https://github.com/pnpm/action-setup/compare/v5...v6)

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- Branch creation
  - Only on Sunday and Saturday (`* * * * 0,6`)
- Automerge
  - Between 12:00 AM and 03:59 AM (`* 0-3 * * *`)

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0My4xMTAuMTIiLCJ1cGRhdGVkSW5WZXIiOiI0My4xMTAuMTIiLCJ0YXJnZXRCcmFuY2giOiJtYWluIiwibGFiZWxzIjpbImtpbmQvZGVwZW5kZW5jeSJdfQ==-->

Reviewed-on: https://gitea.com/gitea/helm-actions/pulls/129
Co-authored-by: Renovate Bot <renovate-bot@gitea.com>
Co-committed-by: Renovate Bot <renovate-bot@gitea.com>

.gitea/workflows/test-pr.yml

@@ -23,7 +23,7 @@ jobs:
           apk update
           apk add --update bash make nodejs npm yamllint ncurses
       - name: Install pnpm
-        uses: pnpm/action-setup@v5
+        uses: pnpm/action-setup@v6
         with:
           version: 10
       - uses: actions/checkout@v6