Suggested test: copilot/dispatch-workflow-yaml-extension

## Motivation

Link to the gh-aw PR: github/gh-aw#49230 — `findWorkflowFile` (used by `dispatch-workflow` and `call-workflow` validation) previously only checked `.yml`, silently failing to resolve target workflows defined as `.yaml`. Now both extensions are checked.

## Proposed test

- **Workflow file**: `test-copilot-dispatch-workflow-yaml-ext.md` (dispatches a worker whose lock file is `.yaml`, not `.yml`)
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `dispatch-workflow`
- **Variant**: standard

## Minimal test prompt sketch

Reuse the existing `test-copilot-dispatch-worker` pattern but add (or rename a copy of) the target worker lock file with a `.yaml` extension, then have the agent dispatch it via `safe-outputs.dispatch-workflow`, confirming resolution succeeds despite the non-`.yml` extension.

## New fixtures or secrets needed

A `.yaml`-suffixed worker workflow fixture (copy of `test-copilot-dispatch-worker.lock.yml` renamed to `.yaml`). No new secrets.

## Notes

`test-copilot-call-workflow` currently appears in `fails.txt`, but that failure is unrelated to this specific `.yaml` extension edge case (it predates the fix and exercises the `.yml` path). This test targets the exact regression fixed in gh-aw#49230.

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Start with the existing test-copilot-dispatch-worker pattern and the test-copilot-dispatch-workflow-yaml-ext.md proposal. Add or rename the worker lock fixture to use a .yaml extension, then verify the copilot workflow_dispatch test resolves it through safe-outputs.dispatch-workflow. Done means the dispatch succeeds without requiring new secrets.

Written by the indexing model from the issue text.