Add integration tests for GitHub MCP server

Description:

The action's ability to interact with GitHub via the Model Context Protocol (MCP) server is a critical and complex feature. We need dedicated integration tests to ensure that the action can correctly connect to the MCP server, use its tools (mcp__github__*), and perform actions against the GitHub API.

Testing Strategy:

1. Create a dedicated workflow in a testing repository. This workflow should be triggered by an event like a new issue being created.
2. Configure the workflow to use the run-gemini-cli action with the mcpServers input pointing to the ghcr.io/github/github-mcp-server image.
3. Provide a prompt that requires the use of an MCP tool.
4. Add a verification step to the workflow. This step will run after the action and use the standard GitHub API (e.g., via the gh CLI) to verify that the expected action was performed (e.g., that the comment was actually added to the issue).