chore(deps): bump skopeo/stable in /tests in the docker-tests group

Bumps the docker-tests group in /tests with 1 update: [skopeo/stable](https://github.com/containers/image_build).


Updates `skopeo/stable` from v1.18.0 to v1.19.0
- [Commits](https://github.com/containers/image_build/commits)

---
updated-dependencies:
- dependency-name: skopeo/stable
  dependency-version: v1.19.0
  dependency-type: direct:production
  dependency-group: docker-tests
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

tests/Dockerfile

@@ -3,7 +3,7 @@
 FROM kindest/node:v1.33.1@sha256:050072256b9a903bd914c0b2866828150cb229cea0efe5892e2b644d5dd3b34f
 
 # this is here so we can grab the latest version of skopeo and have dependabot keep it up to date
-FROM quay.io/skopeo/stable:v1.18.0
+FROM quay.io/skopeo/stable:v1.19.0
 
 FROM python:3.13@sha256:a4b2b11a9faf847c52ad07f5e0d4f34da59bad9d8589b8f2c476165d94c6b377