Version Chooser: Integrate most recent changes from pydata-sphinx-theme

> 1. don't return false, use event.prevent_default() instead
> 2. the fetch().then().catch() pattern you've copied here doesn't actually work as
>    advertised. See the updated logic, which includes an if (head.ok) conditional to
>    distinguish between "successful fetch of desired head (2xx response)" versus
>    "successful fetch of the 404 page (4xx response)". The catch clause is still needed to
>    handle genuine errors (like the fetch being blocked by CORS policy).

Thank you, @drammock.

CHANGES.rst

@@ -6,7 +6,8 @@ CHANGES
 Unreleased
 ----------
 
-- Add version chooser JavaScript helpers derived from ``pydata-sphinx-theme``
+- Add version chooser JavaScript helpers derived from ``pydata-sphinx-theme``.
+  Thanks, @drammock.
 
 
 2023/09/01 0.29.5

src/crate/theme/rtd/crate/version_chooser.html

@@ -8,23 +8,24 @@
     // BSD 3-Clause License; Copyright (c) 2018, pandas; All rights reserved.
     // See `version-switcher.html` and `pydata-sphinx-theme.js`.
 
-    function checkPageExistsAndRedirect(event) {
+    async function checkPageExistsAndRedirect(event) {
+      // Make sure not to follow the original link.
+      event.preventDefault();
       const currentFilePath = `{{ pagename }}.html`,
-        tryUrl = event.target.getAttribute("href");
+        tryUrl = event.currentTarget.getAttribute("href");
       let otherDocsHomepage = tryUrl.replace(currentFilePath, "");
 
-      fetch(tryUrl, { method: "HEAD" })
-        .then(() => {
-          location.href = tryUrl;
-        }) // if the page exists, go there
-        .catch((error) => {
+      try {
+        let head = await fetch(tryUrl, { method: "HEAD" });
+        if (head.ok) {
+          location.href = tryUrl; // the page exists, go there
+        } else {
           location.href = otherDocsHomepage;
-        });
-
-      // Cancel browser's native event handling.
-      // Prevent the browser from following the href of the clicked node,
-      // which is fine because this function takes care of redirecting.
-      return false;
+        }
+      } catch (err) {
+        // something went wrong, probably CORS restriction, fallback to other docs homepage
+        location.href = otherDocsHomepage;
+      }
     }
 
     function versionChooserAppendItem(slug, url) {