Split partial of country select

Background

ee/views/trials/new.html.haml recently changed and jh/views/trials/new.html.haml cause a error since the diveraged.

See https://gitlab.com/gitlab-jh/customers-gitlab-cn/-/issues/95#note_655888106

Fix

This MR split the minimal change from upstream to jh. So JH can just override the two lines of minimal change instead of the entire page.

Keep the change minimal to make sure the affect minimal.

See JH MR gitlab-jh/gitlab!79 (merged)

@godfat-gitlab Could you please review this, thanks.