fix SyntaxWarning

[abcdabcd987]

Python 3.12 raises SyntaxWarning for invalid escape sequence like "\d".

This PR: Use raw strings for the regex and also add a capture group.

Python 3.12.7 | packaged by conda-forge | (main, Oct  4 2024, 16:05:46) [GCC 13.3.0] on linux
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>>> import re
>>> cuda_arch_flags = '-gencode=arch=compute_90,code=compute_90'

>>> int(re.search("compute_\d+", cuda_arch_flags).group()[-2:])
<stdin>:1: SyntaxWarning: invalid escape sequence '\d'
90

>>> int(re.search(r"compute_(\d+)", cuda_arch_flags).group(1))
90