[#370] Fixed sub-navigation active tabindex.

[febdao]

Checklist before requesting a review

• [x] I have formatted the subject to include the issue number as [#123] Verb in past tense with a period at the end.
• [x] I have provided information in the Changed section about WHY something was done if this was a bespoke implementation.
• [x] I have performed a self-review of my code.
• [x] I have commented on my code, particularly in hard-to-understand areas.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [x] I have run new and existing relevant tests locally with my changes, and they have passed.
• [x] I have provided screenshots, where applicable.

Changed

1. Fixed sub-navigation active tabindex.

Screenshots

[github-actions[bot]]

🚀 Deployed on https://6730b2f28109c6cacc87a68f--civictheme-uikit.netlify.app

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 13.87%. Comparing base (a6ccd6f) to head (67d43d5). Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
components/00-base/collapsible/collapsible.js	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #423 +/- ## ======================================= Coverage 13.87% 13.87% ======================================= Files 27 27 Lines 1290 1290 Branches 307 307 ======================================= Hits 179 179 Misses 894 894 Partials 217 217 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.