Add test to avoid problems with chart images

[manuelbuil]

Is your feature request related to a problem? Please describe.

From time to time we, humans, introduce image-related bugs into the rke2 code because:

• we forgot to sync helm-chart images with airgap images (e.g. Multus docker image version mismatch with the airgap package (v1.27.3+rke2r1) #4480)
• we forgot to add "system-default-registry" bits into the chart (e.g. Cilium 1.12.0 and "system-default-registry” not working #3479)

I think it should be easy to verify with a simple test that a PR is not adding any bug related to these problems. Probably limit its run to PRs that update Dockerfile, which is the file changed to update charts.

Describe the solution you'd like

Test that would block the PR because it is adding a bug related to chart images

Describe alternatives you've considered

Additional context

[thomasferrandiz]

/backport v1.26.11+rke2r1

[thomasferrandiz]

/backport v1.27.8+rke2r1