issue #167: added missing test case in chapter 5 lesson 2

[AhmedHanyGamal]

What kind of change does this PR introduce?
It simply adds a test case in the Mutual Dependency lesson

Issue Number:

• Closes Mutual Dependency lesson is missing a test case #167

Summary
The “Mutual Dependency” lesson in Tour of JSON Schema lacked a proper test case to illustrate the difference between a mutual-dependency schema and one that simply uses the required keyword
Because of that, a schema could pass the lesson even though it should have failed or behaved differently under “mutual dependency” rules

I solved this issue by adding the following test case to the lesson

{
  "name": "John Doe"
}