parse-maintainers: Mark as executable

[ Upstream commit 611d61f9 ]

This makes the script more convenient to run.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>