Describe the bug

The following PR: #2726 introduced a breaking change to BTabs component where setting initial index is no longer working, it's being ignored and simply reset to 0 now (in our app it defaults to -1 for some reason). Reproduction contains a paste from the docs where we preset the tabIndex to 2 and you can see that it just resets it back to 0 anyway.

Reproduction

https://stackblitz.com/edit/github-msadvr4m?file=src%2Fcomponents%2FComp.vue

Used Package Manager

pnpm