reset_merge_request_approvals() can reset the approvals of an MR using
the Gitlab API. It only needs to do this if the Gitlab project is not
configured to do it automatically. In this case the function will assume
there is a special API key environment var and use it to create a new
gl_instance and gl_project. The problem is it tries to create these new
instances even when the project handles the approvals reset and that
will always fail because in those instances (kernel-ark) there is no
special API key available.

Fix this by only creating the new instances when reset_approvals_on_push
is not set on the project.

Signed-off-by: Patrick Talbert <ptalbert@redhat.com>