Fix release version for smartcard auth in doc

What does this MR do?

Since smartcard auth was implemented behind a feature flag, the plan was to ship it in 11.5 even if it was merged after the feature freeze. In the end, it wasn't picked, so this MR updates the release version in the documentation.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/726

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer