[4.3] Missing colors language debugbar

[heelc29]

Steps to reproduce the issue

• Enable language debug
• Open debug bar

<tr>
    <td>joomla</td>
    <td>
        <ul>
            <li class="alert-success">+ \administrator/language/en-GB/joomla.ini</li>
        </ul>
    </td>
</tr>

Expected result

.alert-success {
  color: #294b32;
  background-color: #dae5dd;
  border-color: #c7d8cc;
}

Actual result

.alert-success {
  --alert-color: #294b32;
  --alert-bg: #dae5dd;
  --alert-border-color: #c7d8cc;
}

System information (as much as possible)

J4.3-dev

Additional comments

If I revert PR #39379 (Bootstrap update) it works @dgrammatiko

[dgrammatiko]

@heelc29 check #39652

[heelc29]

Thanks