Validate resource_state_events.namespace_id FK

What does this MR do and why?

The final step for adding the sharing key on resource_state_events after the backfill was finalized in !199039 (merged)

Migration output

main: == [advisory_lock_connection] object_id: 146560, pg_backend_pid: 39104
main: == 20250806195249 ValidateResourceStateEventsNamespaceIdForeignKey: migrating =
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0004s
main: -- execute("ALTER TABLE resource_state_events VALIDATE CONSTRAINT fk_20262abeba;")
main:    -> 0.0140s
main: -- execute("RESET statement_timeout")
main:    -> 0.0060s
main: == 20250806195249 ValidateResourceStateEventsNamespaceIdForeignKey: migrated (0.0948s) 

main: == [advisory_lock_connection] object_id: 146560, pg_backend_pid: 39104
ci: == [advisory_lock_connection] object_id: 146560, pg_backend_pid: 39105
ci: == 20250806195249 ValidateResourceStateEventsNamespaceIdForeignKey: migrating =
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0004s
ci: -- execute("ALTER TABLE resource_state_events VALIDATE CONSTRAINT fk_20262abeba;")
ci:    -> 0.0154s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0003s
ci: == 20250806195249 ValidateResourceStateEventsNamespaceIdForeignKey: migrated (0.0529s) 

ci: == [advisory_lock_connection] object_id: 146560, pg_backend_pid: 39105

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Related to #514592 (closed)