sigstore-conformance: add jku as maintainer

[woodruffw]

Per Slack discussion: this adds another maintainer to https://github.com/sigstore-conformance/extremely-dangerous-public-oidc-beacon.

Specifically, it adds @jku (who is already a Sigstore contributor + trusted reviewer).

Shouldn't be merged until @jku actually agrees to accept the maintain bit here -- I don't want to sign him up for things arbitrarily. This is mostly to make sure that PRs to this repo have a slightly larger reviewer timezone window (since I'm US EST and @tetsuo-cpp is Australia EST).

[github-actions]

🍹 preview on sigstore-github-sync/sigstore/github-sigstore-conformance

Pulumi report

Previewing update (sigstore/github-sigstore-conformance)

View Live: https://app.pulumi.com/sigstore/sigstore-github-sync/github-sigstore-conformance/previews/f702ef50-b97a-4de4-bda3-88f552d6bb47

@ Previewing update......
pulumi:pulumi:Stack: (same)
[urn=urn:pulumi:github-sigstore-conformance::sigstore-github-sync::pulumi:pulumi:Stack::sigstore-github-sync-github-sigstore-conformance]
+ github:index/repositoryCollaborator:RepositoryCollaborator: (create)
    [urn=urn:pulumi:github-sigstore-conformance::sigstore-github-sync::github:index/repositoryCollaborator:RepositoryCollaborator::extremely-dangerous-public-oidc-beacon-jku]
    permission               : "maintain"
    permissionDiffSuppression: false
    repository               : "extremely-dangerous-public-oidc-beacon"
    username                 : "jku"
Resources:
+ 1 to create
15 unchanged

[jku]

Looks good to me 👍

[woodruffw]

Thanks @jku! CC @cpanato @haydentherapper for approval 🙂

[haydentherapper]

I have no power to approve :)

[cpanato]

I think next step is to create a team and add the maintainers there.
I will do that