Since Python 3.12, invalid escape sequences produce a SyntaxWarning;
in the future, they will produce SyntaxError.
Using raw strings clear out the warning.
Below the command used for checking the fix worked.
```
$ python3 util/lint/checkpatch_json.py
```
Link: https://docs.python.org/3.12/whatsnew/3.12.html#other-language-changes
Change-Id: I0177dc7f0d3013759879320afdb6ab548d356bc7
Signed-off-by: Ariel Otilibili <otilibil@eurecom.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85771
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
