input: Write a python function to return a greeting string given a name and age.
  assert greeting("John", 28) == "Hi, my name is John and I'm 28 years old."
  assert greeting("Alice", 30) == "Hi, my name is Alice and I'm 30 years old."
  assert greeting("Bob", 22) == "Hi, my name is Bob and I'm 22 years old."
output: def greeting(name, age):
      return f"Hi, my name is {name} and I'm {age} years old."