input: Write a function named `sum_two_variables` that calculates the sum of two variables using a lambda function in Python. The function should return the result of the lambda function. The input to the function will be two integers, and the output will be their sum.
  
  assert sum_two_variables(3, 4) == 7
  assert sum_two_variables(0, 0) == 0
  assert sum_two_variables(-1, 1) == 0
  assert sum_two_variables(-5, -3) == -8
  assert sum_two_variables(10, -2) == 8
output: sum_two_variables = lambda a, b: a + b