feat: update publish.yml checkout repository so there is access to Do…

…ckerfile (supabase#1419)

## What kind of change does this PR introduce?

Currently, the `Dockerfile` can't be read as the [repository might not
be
cloned](https://github.com/supabase/gotrue/actions/runs/7869435581/job/21468831486#step:4:42)

This PR downloads the repository to allow access to the `Dockerfile`

.github/workflows/publish.yml

@@ -15,6 +15,9 @@ jobs:
       packages: write
       id-token: write
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
       - id: meta
         uses: docker/metadata-action@v4
         with: