Suggested test: copilot/create-pull-request-auto-merge-strategy

## Motivation

github/gh-aw#49412 — `safe-outputs.create-pull-request.auto-merge` now accepts explicit merge strategies (`squash`, `merge`, `rebase`) in addition to the existing boolean, mapping to GraphQL `PullRequestMergeMethod` for `enablePullRequestAutoMerge`. Fixes github/gh-aw#49377.

## Proposed test

- **Workflow file**: `test-copilot-create-pull-request-auto-merge.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `create-pull-request` with `auto-merge: squash`
- **Variant**: standard

## Minimal test prompt sketch

Copy `test-copilot-create-pull-request.md`'s structure, add `auto-merge: squash` under `safe-outputs.create-pull-request`, and use a `samples:` block so it's deterministic. The agent creates a small PR; assertion is that the compiled lock file/PR request includes the auto-merge GraphQL call with the squash strategy.

## New fixtures or secrets needed

None — reuses the main repo. Auto-merge itself may require branch protection/settings enabling auto-merge on `githubnext/gh-aw-test`; verify this is already enabled (existing PR tests don't need it since they don't request auto-merge).

## Notes

No existing test exercises `auto-merge` at all (checked `existing-tests.json` and `create-pull-request*` variants — none reference it). If native GitHub auto-merge can't actually complete in a test repo without additional approvals, this test may only be able to assert the safe-output *request* succeeded, not that the PR actually merged.

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Start with test-copilot-create-pull-request-auto-merge.md and compare its structure with the proposed test details. Add the deterministic samples block and auto-merge: squash, then run the workflow and verify that the compiled lock file or PR request includes the auto-merge GraphQL call with the squash strategy; confirm whether the test repository permits auto-merge.

Written by the indexing model from the issue text.