fix: update milestone pr script

[317brian]

Description

Fixes the following warning in the get-milestone-prs.py script:

./distribution/bin/get-milestone-prs.py:45: SyntaxWarning: invalid escape sequence '\w'
  match_result = re.match("(\w+) .*", previous_branch_first_commit)

Python 3.12 upgraded it to a SyntaxWarning from a DeprecationWarning and it'll eventually be a failure

Release note

n/a

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This PR has:

• been self-reviewed.