Suggested test: copilot/create-pull-request-dynamic-assignee

## Motivation

Link to the gh-aw PR: github/gh-aw#42621 — feat: support runtime/dynamic reviewers, team-reviewers, and assignees in `create-pull-request`

`reviewers`, `team-reviewers`, and `assignees` on `create-pull-request` previously only accepted static lists. PR #42621 upgraded these fields to `TemplatableStringSlice`, enabling `${{ }}` expression passthrough. It also fixed a bug where `assignees` was only applied to fallback issues, not to the created PR itself. No existing test exercises expression-valued `assignees` (or `reviewers`) on the `create-pull-request` safe-output.

## Proposed test

- **Workflow file**: `test-copilot-create-pull-request-dynamic-assignee.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `create-pull-request`
- **Variant**: standard

## Minimal test prompt sketch

Ask the agent to create a small file and open a pull request. Configure `assignees: "${{ github.actor }}"` in the safe-output frontmatter so the created PR is automatically assigned to the dispatch actor. Verify the PR title carries the expected prefix and the actor is listed as an assignee.

## New fixtures or secrets needed

None. `github.actor` is available from the dispatch context and is always a collaborator with write access.

## Notes

- `test-copilot-create-pull-request.md` uses static `labels` only; no existing test passes expression-valued `assignees` or `reviewers` to `create-pull-request`.
- `test-copilot-add-reviewer.md` and `test-copilot-assign-to-user.md` use different safe-output types and do not cover the `assignees` field on `create-pull-request` itself.
- PR #42621 also fixed a regression where `assignees` was not applied to the created PR — this test would serve as a regression guard.
- All three engines should eventually get this coverage; proposing the copilot variant first.

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `awmgmcpg`
>> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "awmgmcpg"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [🔍 Suggest New E2E Tests](https://github.com/githubnext/gh-aw-test/actions/runs/28508312058) · 49.8 AIC · ⌖ 6.78 AIC · ⊞ 5.6K · [◷](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 by comparing test-copilot-create-pull-request.md with test-copilot-add-reviewer.md and test-copilot-assign-to-user.md. Add the proposed workflow in test-copilot-create-pull-request-dynamic-assignee.md with a workflow_dispatch trigger and the copilot create-pull-request safe output. Done means the dispatched workflow creates the requested file and PR, applies the expected title prefix, and assigns github.actor.

Written by the indexing model from the issue text.