[gitlab-ingress-nginx chart] Image digest is unusable if tag is overwritten

Summary

The digest for the gitlab-ingress-nginx chart is referenced in the example UBI values file.

This digest is no longer usable if a newer pipeline overwrites the tag. Example:

Job pushed 44233b030d0d4d2c1d2e59d56 digest
Next job pushed ac77552a7ace8645eaccd8ffa digest

Once the second job ran, the digest from the first job is no longer available to pull.

Steps to reproduce

$ # digest from older job
$ docker pull registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller:v1.2.1-ubi8@sha256:44233b030d0d4d2c1d2e59d5695489cb56bb912161342d3c7f5cb1ef046173cd
Error response from daemon: manifest for registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller@sha256:44233b030d0d4d2c1d2e59d5695489cb56bb912161342d3c7f5cb1ef046173cd not found: manifest unknown: manifest unknown

$ # digest from newer job
$ docker pull registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller:v1.2.1-ubi8@sha256:ac77552a7ace8645eaccd8ffa23129a427ec3373e14836f8790a92616a0ec817
registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller@sha256:ac77552a7ace8645eaccd8ffa23129a427ec3373e14836f8790a92616a0ec817: Pulling from gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller
Digest: sha256:ac77552a7ace8645eaccd8ffa23129a427ec3373e14836f8790a92616a0ec817
Status: Image is up to date for registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller@sha256:ac77552a7ace8645eaccd8ffa23129a427ec3373e14836f8790a92616a0ec817
registry.gitlab.com/gitlab-org/cloud-native/charts/gitlab-ingress-nginx/controller:v1.2.1-ubi8@sha256:ac77552a7ace8645eaccd8ffa23129a427ec3373e14836f8790a92616a0ec817

Current behavior

Image digest is no longer usable if tag is overwritten.

Expected behavior

Image digest is still usable if tag is overwritten.