input: Write a function to count the occurrences of each character in a given text.
  assert count_letters('Hello, World!') == {'H': 1, 'e': 1, 'l': 3, 'o': 2, ',': 1, ' ': 1, 'W': 1, 'r': 1, 'd': 1, '!': 1}
  assert count_letters('aaaaa') == {'a': 5}
  assert count_letters('abc123') == {'a': 1, 'b': 1, 'c': 1, '1': 1, '2': 1, '3': 1}
output: def count_letters(text):
      count = {}
      for char in text:
          if char in count:
              count[char] += 1
          else:
              count[char] = 1
      return count