fix: pass empty arguments object in tools-call-simple-text scenario

The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.

Author: alu

src/scenarios/server/tools.ts

@@ -121,8 +121,8 @@ Implement tool \`test_simple_text\` with no arguments that returns:
       const connection = await connectToServer(serverUrl);
 
       const result = await connection.client.callTool({
-        name: 'test_simple_text'
-        /* omit arguments as it is not required in the schema */
+        name: 'test_simple_text',
+        arguments: {}
       });
 
       // Validate response