Update milestone for VS Code item

A teammate noticed that https://docs.gitlab.com/ee/user/project/repository/#clone-and-open-in-visual-studio-code said the feature was released in %13.8, but both of these say %13.10:

• https://about.gitlab.com/releases/2021/03/22/gitlab-13-10-released/#open-project-in-visual-studio-code
• #220957 (closed)

This teensy merge request updates the milestone release info to 13.10.

• Related to #220957 (closed)
• Closes #325575 (closed)