refactor: add width macro footer option govuk-grid-column-one-third

* This is in response to bumping our version of `govuk-frontend`: https://github.com/alphagov/govuk-frontend/blob/main/CHANGELOG.md#check-your-footer-displays-as-expected
* The original PR which forces the change: alphagov/govuk-frontend#2462

app/views/layouts/application.html.erb

@@ -66,7 +66,7 @@
     <footer class="govuk-footer " role="contentinfo">
       <div class="govuk-width-container ">
         <div class="govuk-footer__navigation">
-          <div class="govuk-footer__section">
+          <div class="govuk-footer__section govuk-grid-column-one-third">
             <h2 class="govuk-footer__heading govuk-heading-m">About</h2>
             <ul class="govuk-footer__list govuk-footer__list--columns-1">
               <li class="govuk-footer__list-item">
@@ -80,7 +80,7 @@
               </li>
             </ul>
           </div>
-          <div class="govuk-footer__section">
+          <div class="govuk-footer__section govuk-grid-column-one-third">
             <h2 class="govuk-footer__heading govuk-heading-m">Connect</h2>
             <ul class="govuk-footer__list govuk-footer__list--columns-1">
               <li class="govuk-footer__list-item">
@@ -94,7 +94,7 @@
               </li>
             </ul>
           </div>
-          <div class="govuk-footer__section">
+          <div class="govuk-footer__section govuk-grid-column-one-third">
             <h2 class="govuk-footer__heading govuk-heading-m">Admin</h2>
             <ul class="govuk-footer__list govuk-footer__list--columns-1">
               <li class="govuk-footer__list-item">