package/gitlab-runner: fix forcing openssl

We can't use BR2_PACKAGE_LIBOPENSSL to force selecting libopenssl, as
it is part of a choice. Instead, we have a symbol explicitly to force
libopenssl: BR2_PACKAGE_OPENSSL_FORCE_LIBOPENSSL.

Use that.

Reported-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>