try purging PG16 instead?

.github/workflows/test.yml

@@ -28,6 +28,7 @@ jobs:
       - uses: actions/checkout@v4
       - run: |
           date
+          sudo apt purge postgresql-16
           sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'
           wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
           sudo apt-get update