Update GitHub Actions to reference new branch names. (#2336)

diff --git a/.github/workflows/publish_docs.yml b/.github/workflows/publish_docs.yml
index 16ecca0..317f4ec 100644
--- a/.github/workflows/publish_docs.yml
+++ b/.github/workflows/publish_docs.yml
@@ -17,8 +17,7 @@
 on:
   push:
     branches:
-      # This will be switched to main after shifting to a GitHub-first workflow.
-      - google
+      - main
 
 jobs:
   linux:
diff --git a/.github/workflows/synchronize_submodules.yml b/.github/workflows/synchronize_submodules.yml
index cd0aed6..aba1d6c 100644
--- a/.github/workflows/synchronize_submodules.yml
+++ b/.github/workflows/synchronize_submodules.yml
@@ -19,9 +19,6 @@
 on:
   push:
     branches:
-      - master
-      # This branch doesn't exist yet, but may as part of shifting to a
-      # GitHub-first workflow.
       - google
 
 jobs: