Link provider - issues is being opened on the browser instead of VS Code

Testing #6990

Steps to reproduce: 
* Create a new GitHub issues with the following body
    ```
    https://github.com/lszomoru/GitPlayground/pull/22

    #22
    ```
* Open the issues in VS Code
* Click on the first link -> opens pull request in the browser (expected)
* Click on the second link -> opens the pull request in the browser (unexpected)