Task capability not configured at the server level when expected

Initial Checks

I confirm that I'm using the latest version of MCP Python SDK
I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

The enable_tasks() method doesn't properly set the tasks.requests.tools.call capability on the server, causing compatibility issues with clients that assert against server capabilities before attempting task support on a tool invocation.

Identified during strands-agents/sdk-python#1475.

Example Code

Python & MCP Python SDK

Python 3.12.9
MCP SDK 1.25.0