message: fix: Amend link on Ideal Postcodes icon to open source page on Ideal Postcodes website
diff: <li><a href="https://status.ideal-postcodes.co.uk" title="Status Page" target="_blank">Service Status</a></li>
  </ul>
  <ul class="nav navbar-nav navbar-right">
  - <li><a href="https://ideal-postcodes.co.uk" title="Ideal Postcodes" target="_blank">
  + <li><a href="https://ideal-postcodes.co.uk/open_source" title="Ideal Postcodes" target="_blank">
  <img src="images/house-icon.svg" class="header-icon">
  </a></li>
  <li><a href="https://github.com/ideal-postcodes/postcodes.io/" title="GitHub" target="_blank">
  