input: Write a python function to encrypt a given string using SHA-256.
  assert encrypt_string("Hello, World!") == "a591a6d40bf420404a011733cfb7b190d62c65bf0bcda32b60f131a430a92fdd"
  assert encrypt_string("password123") == "ef92b778bafe771e89245b89ecbc3c261ca19f4d77639e9fbac5f726d700f7a0"
  assert encrypt_string("Python is fun!") == "f64b47e2e2d5860b42c3d4fbc4e64e12e1877c93448e8a0d6b2efb926e6a06ff"
output: def encrypt_string(input_string):
      import hashlib
      sha_signature = hashlib.sha256(input_string.encode()).hexdigest()
      return sha_signature