Login error message uses a fake list but should use a semantic list instead [#3171587]

Problem/Motivation

The error message for an incorrect entry on the login form contains text that's formatted as a list. However, this is not actually an HTML list making it more difficult for screenreaders to read.

The following is the current text.

        Oops, there was an error. This may have happened for the following reasons: <br>
        - Invalid username/email and password combination. <br>
        - There has been more than one failed login attempt for this account. It is temporarily blocked. <br>
        - Too many failed login attempts from your computer (IP address). This IP address is temporarily blocked. <br> <br>
        To solve the issue, try using different login information, try again later, or <a href="/user/password">request a new password</a>

Steps to reproduce

Fill in an incorrect username/password on the /user/login page.

Proposed resolution

Change the user login error message to

Oops, there was an error. This may have happened for the following reasons:
        <ul>
          <li>Invalid username/email and password combination. </li>
        <li>There has been more than one failed login attempt for this account. It is temporarily blocked. </li>
        <li>Too many failed login attempts from your computer (IP address). This IP address is temporarily blocked. </li>
  </ul><br>
        To solve the issue, try using different login information, try again later, or <a href="/user/password">request a new password</a>