Fix markdown syntax error in slack.mdx

Remove extra asterisks in mpim:read permission description that were causing test failures.

Author: codegen-sh[bot]

docs/integrations/slack.mdx

@@ -87,7 +87,7 @@ The Codegen Slack integration requires the following permissions to function eff
 ### Core Messaging Permissions
 - **View messages that mention @codegen** - To respond to direct mentions and requests
 - **Read message history in public and private channels** - To understand context and conversation flow
-- **Read direct messages and group chats** (`mpim:read`)** - To enable private conversations with the agent in group DMs and multi-person direct messages
+- **Read direct messages and group chats** (`mpim:read`) - To enable private conversations with the agent in group DMs and multi-person direct messages
 - **Send messages** - To communicate responses and provide updates
 
 ### Enhanced Communication Features