add 33.x to test_release_branches

#test-continuous

PiperOrigin-RevId: 813899513
diff --git a/.github/workflows/test_release_branches.yml b/.github/workflows/test_release_branches.yml
index 1fd07a3..47e8bf2 100644
--- a/.github/workflows/test_release_branches.yml
+++ b/.github/workflows/test_release_branches.yml
@@ -13,7 +13,7 @@
     strategy:
       fail-fast: false
       matrix:
-        branch: [25.x, 29.x, 31.x, 32.x]
+        branch: [25.x, 29.x, 33.x]
     runs-on: ubuntu-latest
     permissions:
       actions: write