Update mdbook to 0.4.17 (#12339)

Update mdbook (the tool used to render the documentation website) to version 0.4.17.

Author: anoadragon453

.github/workflows/docs.yaml

@@ -22,7 +22,7 @@ jobs:
       - name: Setup mdbook
         uses: peaceiris/actions-mdbook@4b5ef36b314c2599664ca107bb8c02412548d79d # v1.1.14
         with:
-          mdbook-version: '0.4.9'
+          mdbook-version: '0.4.17'
 
       - name: Build the documentation
         # mdbook will only create an index.html if we're including docs/README.md in SUMMARY.md.

changelog.d/12339.doc

@@ -0,0 +1 @@
+Upgrade the version of `mdbook` in CI to 0.4.17.