MAINTAINERS: Fix tests/migration maintainers

when executing the following scripts, it throw error message:
$ ./scripts/get_maintainer.pl -f tests/migration/guestperf.py
get_maintainer.pl: No maintainers found, printing recent contributors.
get_maintainer.pl: Do not blindly cc: them on patches!  Use common sense.

add the tests/migration to the "Migration" section of MAINTAINERS

Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <91d5978357fb8709ef61d2030984f7142847037d.1616141556.git.huangy81@chinatelecom.cn>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed