input: Write a python function to make an API call using environment variables for the API key and endpoint.
  assert 'results' in call_api(None)
  assert isinstance(call_api(None), dict)
  assert call_api(None).get('status') == 'success'
output: import os
  import requests
  
  def call_api(data):
      api_key = os.getenv('API_KEY')
      api_endpoint = os.getenv('API_ENDPOINT')
  
      headers = {
          'Authorization': f'Bearer {api_key}',
          'Content-Type': 'application/json'
      }
  
      response = requests.post(api_endpoint, json=data, headers=headers)
      return response.json()