tools: Fix regex syntax warnings with Python 3.12

tools: Fix regex syntax warnings with Python 3.12

Since Python 3.12, invalid escape sequences generate SyntaxWarning.  In the
future, these invalid sequences will raise a SyntaxError, so changed to using
raw string notation.

Link: https://docs.python.org/3/whatsnew/3.12.html#other-language-changes
Fixes: d8f3a67bf98 ("pygrub: further improve grub2 support")
Fixes: dd03048708a ("xen/pygrub: grub2/grub.cfg from RHEL 7 has new commands in menuentry")
Fixes: d1b93ea2615 ("tools/pygrub: Make pygrub understand default entry in string format")
Fixes: 622e368758b ("Add ZFS libfsimage support patch")
Fixes: 02b26c02c7c ("xen/scripts: add cppcheck tool to the xen-analysis.py script")
Fixes: 56c0063f4e7 ("xen/misra: xen-analysis.py: Improve the cppcheck version check")
Signed-off-by: Ariel Otilibili <Ariel.Otilibili-Anieli@eurecom.fr>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>