Fix title underline for CI

Author: jakirkham

src/maintainer/updating_pkgs.rst

@@ -191,7 +191,7 @@ Once built, you can find the finished package in the ``build_artifacts`` directo
 
 
 Downloading prebuilt packages
-----------------
+-----------------------------
 A neat feature that feedstocks have is the ability to `upload packages to the CI provider for testing <https://conda-forge.org/docs/maintainer/conda_forge_yml.html?highlight=store_build_artifacts#azure>`_.
 This is useful when trying out packages built in a PR. But you first need to download these prebuilt packages.