Fix formatting and add newline at end of file

Author: Tithi234

strings/is_isogram.py

@@ -25,3 +25,5 @@ def is_isogram(string: str) -> bool:
     input_str = input("Enter a string ").strip()
     isogram = is_isogram(input_str)
     print(f"{input_str} is {'an' if isogram else 'not an'} isogram.")
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