MAINTAINERS: git://github -> https://github.com for awilliam

Github deprecated the git:// links about a year ago, so let's move to
the https:// URLs instead.

Reported-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://github.blog/2021-09-01-improving-git-protocol-security-github/


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20221013214636.30721-1-palmer@rivosinc.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>