Git : Link to closed branch still appears when viewing pull requests merged (BB-9403)

After merging a pull request and selecting close source branch, a link still appears at the top of the screen with the source branch (now closed) which leads to an error screen since the branch is not visible anymore.

In the attached image, prodpos-303 is the closed branch, but the link still appears when hovering the mouse over it, this is the screen for the previously merged pull request.