Fix governPolicyUpdate passing wrong keyword to UpdateService

What does this MR do and why?

Fixes Mutations::Govern::PolicyUpdate, which currently fails every call with Internal server error: missing keyword: :container.

Two MRs crossed on master:

• !253003 (merged) renamed the Policy Store services' organization: keyword to container: (and updated PolicyCreate, PolicyDelete, the policies resolver, and the REST endpoint).
• !252080 (merged) added the governPolicyUpdate mutation against the old organization: signature.

They merged without a git conflict, so the mutation kept calling PolicyStore::UpdateService.new(organization: ...) while the service requires container:. This broke ee/spec/requests/api/graphql/mutations/govern/policy_update_spec.rb and is blocking master and MR pipelines (see the ci-health incident below).

The fix passes container: organization, matching the sibling mutations and the REST endpoint in ee/lib/api/govern/policies.rb.

References

• CI-health incident (deployment-blocker): gitlab-org/quality/analytics/ci-health-incidents#1267 (closed)
• Example failing job: https://gitlab.com/gitlab-org/gitlab/-/jobs/16405288029
• Causing MRs: !253003 (merged) and !252080 (merged)
• Reported in: !253311 (comment 3811846060)

Screenshots or screen recordings

Not applicable: backend-only change with no UI impact.

Before	After
Mutation raises missing keyword: :container	Mutation updates the policy

How to set up and validate locally

1. Run the previously failing spec:

   bundle exec rspec ee/spec/requests/api/graphql/mutations/govern/policy_update_spec.rb

2. All examples should pass (they currently fail on master with Internal server error: missing keyword: :container).

MR acceptance checklist

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