Suggested test: copilot/dispatch-workflow-ref-override

## Motivation

github/gh-aw#49408 — `dispatch_workflow` safe output now accepts a per-call `ref` field on the payload (`DispatchWorkflowOutput.ref`), which takes highest priority over configured `target-ref`, `GITHUB_HEAD_REF`, and `context.ref`. Branch names are normalized to `refs/heads/`; full refs are passed through as-is.

## Proposed test

- **Workflow file**: `test-copilot-dispatch-workflow-ref-override.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `dispatch-workflow`
- **Variant**: standard

## Minimal test prompt sketch

Similar to existing `test-copilot-dispatch-workflow.md`, but the sample/prompt sets an explicit `ref` (e.g. `"main"` or a test branch name) on the dispatch payload instead of relying on default ref resolution. Assertion: the dispatched worker run shows the overridden ref was used rather than the triggering ref.

## New fixtures or secrets needed

None — reuses `test-copilot-dispatch-worker` as the target workflow, same as the existing dispatch-workflow test.

## Notes

Existing `test-copilot-dispatch-workflow.md` only exercises default ref resolution (dispatches from current context, no explicit `ref` in payload). This new test exercises the new per-call override specifically. No open suggestion or failing test currently covers this.

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Start with the existing test-copilot-dispatch-workflow.md and the test-copilot-dispatch-worker target workflow, then create test-copilot-dispatch-workflow-ref-override.md with the specified workflow_dispatch, copilot, and dispatch-workflow configuration. Done means the dispatched worker run shows the explicit payload ref rather than the triggering ref, with no new fixtures or secrets required.

Written by the indexing model from the issue text.