server-stateless doesn't set `mcp-method` etc.

Describe the bug

The server-stateless scenario doesn't set the MCP-Method or MCP-Name headers. These are not part of the test and should be set. Our server is throwing an exception because they are missing which, incorrectly, fails the test.

To Reproduce

1. Run server-stateless and alter your server code or test code to check for missing MCP-Method header.

Expected behavior
The test should always set MCP-Method as this is not part of the test.

Logs

  {
    "id": "sep-2575-request-meta-invalid-missing-client-info",
    "name": "RequestMetaInvalid",
    "description": "Rejects request with _meta missing io.modelcontextprotocol/clientInfo",
    "status": "FAILURE",
    "timestamp": "2026-05-23T17:52:50.571Z",
    "errorMessage": "Expected error code -32602, got -32001",
    "specReferences": [
      {
        "id": "SEP-2575",
        "url": "https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575"
      }
    ],
    "details": {
      "fieldIssue": "missing-client-info",
      "response": {
        "jsonrpc": "2.0",
        "id": 103,
        "error": {
          "code": -32001,
          "message": "Missing required header: MCP-Method"
        }
      }
    }
  }

Start by locating the server-stateless scenario and run it to reproduce the missing-header failure. Update the scenario so requests set the MCP-Method and MCP-Name headers, then verify that the test no longer fails because either header is absent.