Bump ubuntu from 24.04 to 26.04

Bumps ubuntu from 24.04 to 26.04.

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

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

Author: dependabot[bot]

Dockerfile

@@ -177,7 +177,7 @@ LABEL org.opencontainers.image.url="https://hub.docker.com/r/rancher/rke2-runtim
 LABEL org.opencontainers.image.source="https://github.com/rancher/rke2"
 COPY --from=runtime-collect / /
 
-FROM ubuntu:24.04 AS test
+FROM ubuntu:26.04 AS test
 ARG TARGETARCH
 VOLUME /var/lib/rancher/rke2
 VOLUME /var/lib/kubelet