ci: drop master branch requirement for AppVeyor releases

ci: drop master branch requirement for AppVeyor releases

Even if we tag a commit on the master branch AppVeyor won't upload the
installers as GitHub release artifacts.

https://ci.appveyor.com/project/axboe/fio/builds/44416420/job/t1elejqo2yk3r72b

So just drop the requirement for AppVeyor to only upload release
artifacts from the master branch.

This seems to get things working on my fork:

https://ci.appveyor.com/project/vincentkfu/fio/builds/44417490/job/e6xtrwc6xlccrn0j

It's good to have the flexibility to store installers from other
branches in any case.

Signed-off-by: Vincent Fu <vincentfu@gmail.com>