ci) use manual checkout for gitea actions

.gitea/workflows/main-image.yml

@@ -15,10 +15,16 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          github-server-url: https://cloud.campbellwireless.net/git
-          fetch-depth: 0
+        env:
+          REPO_URL: https://cloud.campbellwireless.net/git/${{ github.repository }}.git
+        run: |
+          set -eux
+          git init .
+          git remote add origin "$REPO_URL"
+          auth="$(printf '%s' '${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}' | base64 | tr -d '\n')"
+          git config --local http.https://cloud.campbellwireless.net/.extraheader "AUTHORIZATION: basic $auth"
+          git fetch --prune --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*
+          git checkout --detach "${{ github.sha }}"
 
       - name: Setup Docker Buildx
         uses: docker/setup-buildx-action@v3