Fix github.com/elastic/e2e-testing error

[romulets]

While verifying everything is working as it should after updating dependabot to also handle 8.x branch, I noticed that dependabot has been failing for a while on the dependency github.com/elastic/[email protected] with error

Handled error whilst updating github.com/elastic/e2e-testing: dependency_file_not_resolvable {:message=>"go: downloading github.com/elastic/e2e-testing v1.99.1\ngo: github.com/elastic/[email protected] indirectly requires k8s.io/[email protected]: reading k8s.io/api/go.mod at revision v0.0.0: unknown revision v0.0.0"}

I checked, the k8s.io/api dependency is not on 0.0.0. Once I get what's in the go proxy (https://proxy.golang.org:443/github.com/elastic/e2e-testing/@v/v1.99.1.zip). we get a very very old version of this package.
Could be the problem is because is archived https://github.com/elastic/e2e-testing/tree/main.

Regardless, I think it's nice if we have a look and fix it. We use this dependency only in the mage agent-package command to fetch beats binary.

It's non blocking, because the dependabot still works for the other dependencies. It's just an error we get