Update collaborators for sigstore-conformance

[di]

Adds @jku, removes @apstickler.

(cc @woodruffw, @haydentherapper)

[haydentherapper]

cc tsc @bobcallaway @trevrosen @lukehinds @priyawadhwa @SantiagoTorres

[github-actions]

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

Pulumi report

Previewing update (sigstore/github-prod)

View Live: https://app.pulumi.com/sigstore/sigstore-github-sync/github-prod/previews/59e7a69a-ce6a-4bc0-9fea-6665814f0c7f

@ Previewing update.......
pulumi:pulumi:Stack: (same)
[urn=urn:pulumi:github-prod::sigstore-github-sync::pulumi:pulumi:Stack::sigstore-github-sync-github-prod]
@ Previewing update....
+ github:index/repositoryCollaborator:RepositoryCollaborator: (create)
    [urn=urn:pulumi:github-prod::sigstore-github-sync::github:index/repositoryCollaborator:RepositoryCollaborator::sigstore-conformance-jku]
    permission               : "push"
    permissionDiffSuppression: false
    repository               : "sigstore-conformance"
    username                 : "jku"
- github:index/repositoryCollaborator:RepositoryCollaborator: (delete)
    [id=sigstore-conformance:apstickler]
    [urn=urn:pulumi:github-prod::sigstore-github-sync::github:index/repositoryCollaborator:RepositoryCollaborator::sigstore-conformance-apstickler]
    permission               : "admin"
    permissionDiffSuppression: false
    repository               : "sigstore-conformance"
    username                 : "apstickler"
Resources:
+ 1 to create
- 1 to delete
2 changes. 564 unchanged