Update sigstore/cosign-installer digest to c56c2d3 (#29293)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/docker.yaml

@@ -22,7 +22,7 @@ jobs:
                   fetch-depth: 0 # needed for docker-package to be able to calculate the version
 
             - name: Install Cosign
-              uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # v3
+              uses: sigstore/cosign-installer@c56c2d3e59e4281cc41dea2217323ba5694b171e # v3
 
             - name: Set up QEMU
               uses: docker/setup-qemu-action@53851d14592bedcffcf25ea515637cff71ef929a # v3