feat: Ensure the page loading has sticky footer.

Reached out to support for this. It appears the page loading doesn't take changes in for the `brand-openedx` CSS changes, so we need to adjust the height manually.

https://discuss.openedx.org/t/sticky-footer-mfe-learning-page-loading/12721

src/generic/PageLoading.jsx

@@ -22,7 +22,7 @@ export default class PageLoading extends Component {
         <div
           className="d-flex justify-content-center align-items-center flex-column"
           style={{
-            height: '50vh',
+            height: '89vh',
           }}
         >
           <Spinner animation="border" variant="primary" role="status">