Fix docker digest in CI workflow

Author: JonnyWong16

.github/workflows/ci.yaml

@@ -129,7 +129,7 @@ jobs:
           --header "Accept: application/vnd.docker.distribution.manifest.v2+json" \
           --header "Authorization: Bearer $token" \
           "https://registry-1.docker.io/v2/${{ env.PLEX_CONTAINER }}/manifests/${{ env.PLEX_CONTAINER_TAG }}" \
-          | jq -r '.config.digest')
+          | sha256sum)
         echo "Digest: $digest"
         echo "digest=$digest" >> $GITHUB_OUTPUT