Merging upstream version 5.3.5+dfsg.

Signed-off-by: Daniel Baumann <daniel@debian.org>

site/content/docs/5.3/examples/checkout/index.html

@@ -5,6 +5,7 @@ extra_css:
   - "checkout.css"
 extra_js:
   - src: "checkout.js"
+    defer: true
 body_class: "bg-body-tertiary"
 ---
 
@@ -12,7 +13,7 @@ body_class: "bg-body-tertiary"
   <main>
     <div class="py-5 text-center">
       <img class="d-block mx-auto mb-4" src="/docs/{{< param docs_version >}}/assets/brand/bootstrap-logo.svg" alt="" width="72" height="57">
-      <h2>Checkout form</h2>
+      <h1 class="h2">Checkout form</h1>
       <p class="lead">Below is an example form built entirely with Bootstrap’s form controls. Each required form group has a validation state that can be triggered by attempting to submit the form without completing it.</p>
     </div>