Plumb GH_TOKEN to Acquisition outerloop/integration tests via test properties bag

## Summary

The Acquisition test project (`tests/Aspire.Acquisition.Tests`) includes outerloop integration tests (`PRScriptIntegrationTests`) that require `GH_TOKEN` to call real GitHub APIs. Currently, the token is not provided to these tests when run in the outerloop workflow.

In PR #15995, we removed the `|| inputs.testShortName == 'Acquisition'` special-case from `run-tests.yml` to avoid unnecessarily exposing `GH_TOKEN` to the normal (non-outerloop) Acquisition tests, which use mock `gh` scripts and don't need the token.

## What's Needed

Once #16056 (generic properties bag for test pipeline) is merged, add a `requiresGhToken` MSBuild property to the Acquisition test project so the outerloop workflow can provide `GH_TOKEN` without hardcoding test names in the workflow YAML.

## Blocked By

- #16056 — Simplify test pipeline flag plumbing with a generic properties bag

## Context

- PR #15995 — Add comprehensive test coverage for CLI acquisition scripts
- The outerloop integration tests self-skip gracefully when `GH_TOKEN` is absent (`Assert.Skip`), so this is not blocking any CI runs.