microk8s ctr image pull fails to pull image from GitLab private registry

Summary

While troubleshooting why microk8s failed to pull images from a private registry I own in GitLab, I tried manually pulling the container image with ctr image pull using a GitLab project access token with the following command:

~# microk8s ctr image pull --user <username> registry.gitlab.com/<username>/<project>:<tag>

The command shown above fails with the following error:

Password: me@somehostname:~# microk8s ctr image pull --user <username> registry.gitlab.com/<username>/<project>:latest
Password: 
registry.gitlab.com/<username>/<project>:latest: resolving      |--------------------------------------| 
elapsed: 0.7 s                                      total:   0.0 B (0.0 B/s)                                         
INFO[0007] trying next host                              error="failed to authorize: failed to fetch oauth token: unexpected status from GET request to https://gitlab.com/jwt/auth?scope=repository%3A<username>%2F<project>%3Apull&service=container_registry: 403 Forbidden" host=registry.gitlab.com
ctr: failed to resolve reference "registry.gitlab.com/<username>/<project>:latest": failed to authorize: failed to fetch oauth token: unexpected status from GET request to https://gitlab.com/jwt/auth?scope=repository%3A<username>%2F<project>%3Apull&service=container_registry: 403 Forbidden

What Should Happen Instead?

The container image should be pulled. Docker is able to pull the image by first logging in with the same username:password used with containerd.

Reproduction Steps

microk8s ctr image pull --user <username> registry.gitlab.com/<username>/<project>:<tag>