chore(deps): bump ubuntu from b7f4819 to 678c655 in /gitlab (#118)

Bumps ubuntu from `b7f4819` to `678c655`.

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-version: '26.04'
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

gitlab/Dockerfile

@@ -6,7 +6,7 @@
 # Source: https://github.com/tspuhler/LTROPS-2341 (docker/Dockerfile)
 
 # Pinned multi-arch index digest (docker buildx imagetools inspect ubuntu:24.04)
-FROM ubuntu:26.04@sha256:b7f48194d4d8b763a478a621cdc81c27be222ba2206ca3ca6bc42b49685f3d9e
+FROM ubuntu:26.04@sha256:678c6550cc43645e08669028bc177f50be4e7c5b8cca677067b1914d4afc7a03
 
 ENV DEBIAN_FRONTEND=noninteractive