`--add-github-mcp-tool=create_pull_request` leaves the configured endpoint readonly

[CezaryKlus]

Describe the bug

--add-github-mcp-tool argument still makes the github-mcp-server pointing to read only endpoint /mcp/readonly
Therefore tool is not added.

Affected version

1.0.39

Steps to reproduce the behavior

1. Run copilot with --add-github-mcp-tool=create_pull_request
2. Observe in github-mcp-server tool is not added
3. Observe URL pointing to read only endpoint /mcp/readonly

Expected behavior

--add-github-mcp-tool=create_pull_request or any other write tool changes the endpoint to /mcp

Additional context

No response