build(deps): bump library/ubuntu

Bumps the all group in /tekton/images/test-runner with 1 update: library/ubuntu.


Updates `library/ubuntu` from `c4570d2` to `a08e551`

---
updated-dependencies:
- dependency-name: library/ubuntu
  dependency-version: '24.04'
  dependency-type: direct:production
  dependency-group: all
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

tekton/images/test-runner/Dockerfile

@@ -23,7 +23,7 @@ RUN cd /go/src/k8s.io/test-infra && \
     git checkout e685556b32c5fb7ab12c3277d41112d47ceac0cd && \
     go install k8s.io/test-infra/kubetest
 
-FROM docker.io/library/ubuntu:24.04@sha256:c4570d2f4665d5d118ae29fb494dee4f8db8fcfaee0e37a2e19b827f399070d3
+FROM docker.io/library/ubuntu:24.04@sha256:a08e551cb33850e4740772b38217fc1796a66da2506d312abe51acda354ff061
 ARG GO_VERSION
 LABEL maintainer "Tekton Authors <tekton-dev@googlegroups.com>"
 LABEL org.opencontainers.image.source=https://github.com/tektoncd/plumbing