maths/greatest_common_divisor: fix Python 3 except syntax

`except IndexError, UnboundLocalError, ValueError:` is Python 2
syntax and raises SyntaxError under Python 3. The module currently
fails to import at all, and downstream modules that depend on it
(maths.least_common_multiple, maths.primelib) also fail with
ImportError.

Restore the parenthesised tuple form `except (IndexError,
UnboundLocalError, ValueError):`, which was the correct form before
a recent pre-commit autoupdate stripped the parentheses.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thejesh23

maths/greatest_common_divisor.py

@@ -73,7 +73,7 @@ def main():
             f"{greatest_common_divisor(num_1, num_2)}"
         )
         print(f"By iterative gcd({num_1}, {num_2}) = {gcd_by_iterative(num_1, num_2)}")
-    except IndexError, UnboundLocalError, ValueError:
+    except (IndexError, UnboundLocalError, ValueError):
         print("Wrong input")