Fix(a11y/tabs) : move focusable element from <li> to <a>

[XinaICBF]

issue: 2171 issue: 2354 This PR addresses accessibility issues in the Tabs widget.

• Moves focus from
• elements to elements.
• Resolves the "nested interactive controls" warning raised by accessibility testing tools.
• Aligns with WAI-ARIA Authoring Practices for tabs.