Resolve #3613843 "Follow the Orchestra pending-actions finder move to the base module"

Follows Orchestra #3613841, which moves PendingActionsFinder out of orchestra_ui into its base module.

The finder answers "what may this account act on right now". That is not a UI concern, and this module is the evidence: a booking consumer had to reach into Orchestra's admin UI for a service about work items. Orchestra's own personal Views hit the same wall, which is what forced the move.

Two lines, no behavior change:

• yoyaku_orchestra_order.services.yml: the argument becomes @orchestra.pending_actions.
• OrderWorkflowColumn: the import becomes Drupal\orchestra\PendingActionsFinder.

Postponed on #3613841 landing first, otherwise this breaks against the current Orchestra release.