chore: pinning digest for skopeo image (#354)

Signed-off-by: Niccolò Fei <niccolo.fei@enterprisedb.com>

Author: NiccoloFei

.github/actions/copy-images/action.yml

@@ -29,7 +29,7 @@ runs:
       shell: bash
       env:
         # renovate: datasource=docker depName=quay.io/skopeo/stable versioning=loose
-        SKOPEO_VERSION: "v1.20.0"
+        SKOPEO_VERSION: "v1.20.0@sha256:82dfe13efeaac954590352dd4956473226993254758fa668d6cbb752cb367df7"
         SUFFIX: ${{ inputs.test_registry_suffix }}
       run: |
         images=$(echo '${{ inputs.bake_build_metadata }}' |