Suggested test: copilot/siderepo-push-to-pull-request-branch-wildcard-repo

## Motivation

github/gh-aw#49813 — `push_to_pull_request_branch` gained an explicit `repo` (`owner/repo`) input for disambiguating wildcard (`target: "*"`) targets in multi-repo workflows, since branch resolution previously failed when the PR branch existed only in a side checkout.

## Proposed test

- **Workflow file**: `test-copilot-siderepo-push-to-pull-request-branch-wildcard-repo.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `push_to_pull_request_branch` with `target: "*"` and explicit `repo` field
- **Variant**: siderepo (justified: exercises multi-repo wildcard target disambiguation, requires a side checkout)

## Minimal test prompt sketch

Checkout both the main repo and `githubnext/gh-aw-side-repo`, open (or reuse) a PR branch in the side repo, then call `push_to_pull_request_branch` with `target: "*"` and `repo: githubnext/gh-aw-side-repo` so the tool must use the new `repo` field to resolve the correct checkout instead of falling back to `GITHUB_WORKSPACE`.

## New fixtures or secrets needed

None — reuses existing `githubnext/gh-aw-side-repo` fixture.

## Notes

Existing `test-copilot-siderepo-push-to-pull-request-branch-using-dispatch` is currently failing (see fails.txt) and does not exercise the wildcard `target: "*"` + explicit `repo` disambiguation path added in #49813; this is a distinct scenario, not a duplicate of that failure.

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