ci: use overlay2 storage driver instead of pinning docker v28

Docker 29 itself works; the breakage on the GHA runner image was the
overlayfs default. Setting storage-driver=overlay2 restores the
long-standing default and lets the suite run on the current Docker
without the apt downgrade dance.

Fixes #3094

.github/workflows/integration-test-template.yml

@@ -67,22 +67,10 @@ jobs:
         with:
           name: postgres-image
           path: /tmp/artifacts
-      - name: Pin Docker to v28 (avoid v29 breaking changes)
+      - name: Force overlay2 storage driver
         run: |
-          # Docker 29 breaks docker build via Go client libraries and
-          # docker load/save with certain tarball formats.
-          # Pin to Docker 28.x until our tooling is updated.
-          # https://github.com/actions/runner-images/issues/13474
-          sudo install -m 0755 -d /etc/apt/keyrings
-          curl -fsSL https://download.docker.com/linux/ubuntu/gpg \
-            | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
-          echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] \
-            https://download.docker.com/linux/ubuntu $(. /etc/os-release && echo "$VERSION_CODENAME") stable" \
-            | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
-          sudo apt-get update -qq
-          VERSION=$(apt-cache madison docker-ce | grep '28\.5' | head -1 | awk '{print $3}')
-          sudo apt-get install -y --allow-downgrades \
-            "docker-ce=${VERSION}" "docker-ce-cli=${VERSION}"
+          sudo mkdir -p /etc/docker
+          echo '{"storage-driver":"overlay2"}' | sudo tee /etc/docker/daemon.json
           sudo systemctl restart docker
           docker version
       - name: Load Docker images, Go cache, and prepare binary