[testplan-item] Allow multiple PR description open at once

[alexr00]

Refs #3058

• anyOS @joaomoreno
• anyOS @vijayupadya

Complexity: 1

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Context

The Pull Request extension now allows users to open multiple pull request descriptions in separate editor tabs simultaneously. Previously, opening a new PR description would reuse the existing editor tab instead of creating a new one.

Test Steps

1. Install the latest pre-release version of GitHub Pull Requests
2. Open a folder which contains a GitHub repository
3. Open the Pull Requests view
4. Click on a PR to open it's description
5. Repeat step 2 for a second, different PR
   • A second editor tab should open, showing the description of the second PR
   • Both PR description tabs should remain open and display their respective PRs
6. Switch between the two PR description tabs
   • Each tab should show the correct PR description without reloading or changing content