The ubuntu_version_sync.yml workflow fails with "Invalid workflow file"

[evverx]

In https://github.com/google/oss-fuzz/actions/runs/18799713418 it failed with

Invalid workflow file: .github/workflows/ubuntu_version_sync.yml#L1
(Line: 34, Col: 12): Unexpected symbol: '@'. Located at position 21 within expression: !LEGACY_DOCKERFILES[@]

[jsoref]

• @hunsche feat(ci): Enable parallel builds for Ubuntu 20.04 & 24.04 base images #13964 broke this