Skip backend in docs build

docs/gen_files.py

@@ -18,7 +18,7 @@
         doc_path = doc_path.with_name("index.md")
         full_doc_path = full_doc_path.with_name("index.md")
 
-    if not len(parts) or parts[-1] == "__main__" or parts[0] == "codegen":
+    if not len(parts) or parts[-1] == "__main__" or parts[0] in ("codegen", "backend"):
         continue
 
     with mkdocs_gen_files.open(full_doc_path, "w") as fd: