bug(preview sites): dropdown shows incorrect label for Optimize docs

[pepopowitz]

When viewing a preview site, the dropdown shows the incorrect label when viewing Optimize docs.

In this example, the dropdown should be displaying 8.5/3.13.0 instead of 8.5:

This is happening because the customized NavbarItem sniffs the URL to determine if it should show the current Optimize version label in the dropdown instead of the main docs label. In a preview environment, the URL starts with the PR number (example: https://preview.docs.camunda.cloud/pr-4421/index.html). The regex expects the version number first, and doesn't match, and it always displays the main docs label.