Fix TestUpgradeCommand_UpdatesAgentFiles after agent template removal

[Copilot]

PR #13612 removed embedded template files and switched to downloading agentic-workflows.agent.md from GitHub on demand. The upgrade command no longer creates github-agentic-workflows.md or upgrade-agentic-workflows.md - these files are expected only in the gh-aw repository itself.

Changes

• Removed assertions for files no longer created by upgrade command
• Updated test to verify only dispatcher agent file creation
• Added comment documenting behavior change

// Before: Expected 3 files to be created
assert.FileExists(t, instructionsFile, "Copilot instructions file should be created")
assert.FileExists(t, dispatcherFile, "Dispatcher agent file should be created")
assert.FileExists(t, upgradePromptFile, "Upgrade prompt file should be created")

// After: Only dispatcher agent is downloaded/created
dispatcherFile := filepath.Join(tmpDir, ".github", "agents", "agentic-workflows.agent.md")
assert.FileExists(t, dispatcherFile, "Dispatcher agent file should be created")

Original prompt

Reference: https://github.com/github/gh-aw/actions/runs/21658317320/job/62437868339#step:8:1

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[Copilot]

Pull request overview

This PR fixes the TestUpgradeCommand_UpdatesAgentFiles test to align with behavior changes introduced in PR #13612, which removed embedded template files and switched to downloading the dispatcher agent file from GitHub on demand.

Changes:

• Removed test assertions for github-agentic-workflows.md and upgrade-agentic-workflows.md files that are no longer created
• Updated test to verify only the dispatcher agent file (.github/agents/agentic-workflows.agent.md) is downloaded/created
• Added explanatory comment documenting the behavior change from PR #13612

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