docgen: Generate a tar file for the doc artifact

A tar.xz file is easier to deal with that a zip file containing a tar
file.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

.github/workflows/docs.yml

@@ -70,6 +70,7 @@ jobs:
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
         with:
+          name: rust-lang-html.tar.xz
           path: zephyr-rust-lang/docout
 
   deploy: