Fix deployment jobs using nil token

What does this MR do?

Unfortunately, it seems that the migration to
clusters_kubernetes_namespace still needs to create the new restricted
service accounts and then fetch the tokens. Until that is done, we
cannot use it and have to fall back to the main token from
clusters_platform_kubernetes.

Given that pre-migration clusters were using this main token it should be okay to fall back to it

What are the relevant issue numbers?

Fixes #53879 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• [-] Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.