scripts/build/verinfo.py: use a python raw string for the regular expression

[ksherlock]

so \ chars aren't treated as part of an escape sequence. (It does the right thing but it generates a warning)

python3 ./scripts/build/verinfo.py 
./scripts/build/verinfo.py:26: SyntaxWarning: invalid escape sequence '\s'
  pattern = re.compile('\s+BARE_BUILD_VERSION\s+"(([^."]+)\.([^."]+))"')
usage: verinfo.py [-h] [--target <target>] [--subtarget <subtarget>] [--executable <executable>] [--format <format>] [--resources <resfile>] [-o <outfile>]
                  <srcfile>

[angelosa]

https://pylint.pycqa.org/en/latest/user_guide/messages/warning/anomalous-backslash-in-string.html