Tab: fix a `tabindex` issue

Description

Do the tabindex trick before checking whether the element has the role="tab" or not.

Motivation & Context

I couldn't spot any breaking change.

I tried to change the role of the tab component to make it a menubar but I went into the following issue following those steps:

• Click on the active tab
• Tab and Shift + Tab works well 🟢
• →, Tab and Shift + Tab works but not as expected 🟡
• →, →, Tab and Shift + Tab doesn't work at all 🔴

Is there a need for role="tablist/tab" to make it work/accessible ? If yes, why the behavior still works if I stay on the tabs element ?

Here is the Codepen I used to make some tests:

https://codepen.io/louismaximepiton/pen/oNqOEWG

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38154--twbs-bootstrap.netlify.app/docs/5.3/components/navs-tabs#javascript-behavior

Related issues

Might be linked to #33079.