chore(renovate): track the smoke-test Dockerfile image

[setchy]

Why

Renovate currently skips tests/shell/Dockerfile, so the ubuntu:26.04@sha256:… base image is never kept up to date. The repo inherits config:best-practices, which includes :ignoreModulesAndTests — its global ignorePaths contains **/tests/**, which excludes this Dockerfile during extraction. That is why the Dependency Dashboard (#2) has no dockerfile section.

Change

• renovate.json: give the dockerfile manager its own ignorePaths, scoped to that manager, omitting **/tests/**. A description on the manager records the why inline, since JSON has no comments.

Why scoped to the dockerfile manager

• includePaths can't be used here: ignorePaths takes precedence, so dockerfile.includePaths: ["tests/shell/Dockerfile"] still leaves the file ignored (verified locally).
• An explicit packageRules/matchFileNames rule can't help either: ignore filtering happens during extraction, before package rules run.
• Redefining the global ignorePaths would work but is broader than needed — it would re-include tests/ for every manager (npm, etc.). Scoping it to dockerfile re-includes tests/ for that manager only, while the global **/tests/** ignore stays in place for everything else.

Renovate keeps the version tag alongside the digest and updates both together (default docker:pinDigests behaviour), e.g. ARG GNOME_TEST_IMAGE=ubuntu:26.04@sha256:…. The apt-get install packages are unversioned and skipped (unspecified-version), so no extra PRs are expected.

Validation

• renovate-config-validator — config valid
• Local extraction: the dockerfile manager now extracts tests/shell/Dockerfile (ubuntu, currentValue: 26.04, currentDigest: sha256:cd21…) and generates the tag+digest replacement template
• Local extraction: other managers still ignore tests/ (a tests/fixture/package.json is not picked up)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud