fix(gatsby): fix Uncaught TypeError in navigation.js (gatsbyjs#23196)

* Add null check to address gatsbyjs#21263

gatsbyjs#21263 is an issue many people are arriving at for a variety of reasons.  Since the code contains this logic on the following line:

```
      if (pageHeadings && pageHeadings.length) {
```

There should be no issue in seeing if `document.getElementById(`gatsby-focus-wrapper`) exists first before attempting to look up `getElementsByTagName`.

* Update packages/gatsby/cache-dir/navigation.js

Co-Authored-By: Vladimir Razuvaev <vladimir.razuvaev@gmail.com>

* chore: format

Co-authored-by: Vladimir Razuvaev <vladimir.razuvaev@gmail.com>
Co-authored-by: gatsbybot <mathews.kyle+gatsbybot@gmail.com>

packages/gatsby/cache-dir/navigation.js

@@ -171,9 +171,7 @@ class RouteAnnouncer extends React.Component {
       if (document.title) {
         pageName = document.title
       }
-      const pageHeadings = document
-        .getElementById(`gatsby-focus-wrapper`)
-        .getElementsByTagName(`h1`)
+      const pageHeadings = document.querySelectorAll(`#gatsby-focus-wrapper h1`)
       if (pageHeadings && pageHeadings.length) {
         pageName = pageHeadings[0].textContent
       }