chore: expand CODEOWNERS to default allow platform modifications (#20166)

.github/CODEOWNERS

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index ebef3eb..1f449e2 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -1,7 +1,7 @@
 # Default owner for all directories not owned by others
 # The cloud-sdk-go-team team are the effective repo maintainers, but automatic
 # generation/releasing PRs are in the purview of the librarian team.
-*                       @googleapis/cloud-sdk-go-team
+*                       @googleapis/cloud-sdk-go-team @googleapis/cloud-sdk-librarian-team
 
 /librarian.yaml         @googleapis/cloud-sdk-librarian-team
 /ai/                    @googleapis/vertexai-team @googleapis/cloud-sdk-go-team @googleapis/cloud-sdk-librarian-team