temp: use upcoming-4.2 branch of docs-tools

Author: kay-kim

config/build_conf.yaml

@@ -26,7 +26,7 @@ system:
     - includes: '/source/includes/metadata.yaml'
     - migrations: 'manual-migrations.yaml'
 assets:
-  - branch: master
+  - branch: upcoming-4.2
     path: build/docs-tools
     repository: https://github.com/mongodb/docs-tools.git
 paths: