GH-123945: Update regex for parsing negative numbers that contain underscores (#123970)

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Co-authored-by: Brandt Bucher <brandtbucher@gmail.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

Lib/argparse.py

@@ -1360,7 +1360,7 @@ class _ActionsContainer(object):
         self._defaults = {}
 
         # determines whether an "option" looks like a negative number
-        self._negative_number_matcher = _re.compile(r'^-\d+$|^-\d*\.\d+$')
+        self._negative_number_matcher = _re.compile(r'^-\d[\d_]*(\.\d[\d_]*)?$')
 
         # whether or not there are any optionals that look like negative
         # numbers -- uses a list so it can be shared and edited