Move "active" class from `.nav-item` to `.nav-link`

The "active" CSS class must be on "nav-link" element, see _navbar.scss:

    .nav-link.active {
      color: $navbar-dark-active-color;
    }

Commit 62a0358f (PR #32647) has fixed the issue on a single file, but forgot the others.

cc @XhmikosR