fix: only render secondaryMenu if it should be shown

[hidde]

fixes #10704

Issue was that with keyboard, you could reach the primary menu, while it was made invisible by CSS. By not rendering secondaryMenu based on the secondaryMenuShown logic, , we make sure it isn't accessible by keyboard while it is hidden.

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• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
  • Note from author: I did not find existing tests for the behaviour and did not add new ones. We are dogfooding this change on nldesignsystem.nl (source).
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

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