fix sbom upload rule

Fix: changed dockerfile_path not to include the project dir so

"exists:
        - ${DOCKERFILE_PATH}"

works since it checks relative to project dir. https://docs.gitlab.com/ee/ci/yaml/#rulesexists planning#1388 (closed).

requested review from @Manuel_Menz

assigned to @Pascal_Osterwinter

changed the description

approved this merge request

mentioned in commit fcb1f296

merged