Suggested test: copilot/ambient-folders-top-level-frontmatter

## Motivation

github/gh-aw#50168 — moved the `ambient-folders` workflow field from nested `on.ambient-folders` to a top-level `ambient-folders` frontmatter field. This is a breaking schema/parsing change.

## Proposed test

- **Workflow file**: `test-copilot-ambient-folders.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `create-issue` or `noop`
- **Variant**: standard

## Minimal test prompt sketch

Add a top-level `ambient-folders:` frontmatter field pointing at a small existing repo directory, compile, and have the agent confirm (e.g. via a noop message or issue body) that the ambient folder content was made available in its context.

## New fixtures or secrets needed

None — can reference an existing directory in `githubnext/gh-aw-test` as the ambient folder source.

## Notes

Since this is a breaking schema relocation (old `on.ambient-folders` should now be rejected/ignored), the test is also useful as a regression guard that top-level `ambient-folders` parses correctly across gh-aw refs. Not present in `existing-tests.json` or `open-suggestions.json`.

> Generated by [🔍 Suggest New E2E Tests](https://github.com/githubnext/gh-aw-test/actions/runs/30896082598) · auto · 36.6 AIC · ⌖ 3.13 AIC · ⊞ 8.3K · [◷](https://github.com/search?q=repo%3Agithubnext%2Fgh-aw-test+is%3Aissue+%22gh-aw-workflow-call-id%3A+githubnext%2Fgh-aw-test%2Fsuggest-new-e2e-tests%22&type=issues)

Start with the proposed test file, test-copilot-ambient-folders.md, and compare nearby entries in existing-tests.json and open-suggestions.json. Add the workflow_dispatch copilot case using an existing githubnext/gh-aw-test directory, compile it, and confirm the ambient-folder content reaches the agent; the top-level field should work while the old nested form is rejected or ignored.

Written by the indexing model from the issue text.