Unable to install anthropics/claude-plugins-official marketplace: Invalid marketplace.json: plugins.56.source

### Describe the bug

Unable to install the `anthropics/claude-plugins-official` marketplace using the Copilot CLI.
The command fails with a schema validation error related to `marketplace.json`.

### Affected version

GitHub Copilot CLI 1.0.4

### Steps to reproduce the behavior

1. Run the following command: `copilot plugin marketplace add anthropics/claude-plugins-official`
2. Command fails: `Failed to add marketplace: Invalid marketplace.json: plugins.56.source: Invalid input`

### Expected behavior

Marketplace added successfully.

### Additional context

It appears there have been recent updates to the marketplace.json schema.
A similar issue occurred in the Claude Code and was fixed here:

https://github.com/anthropics/claude-plugins-official/issues/585