Fix syntax error with when statement for build-wheel-mirror
Fix syntax error with when statement for build-wheel-mirror

Doesn't look like --syntax-check or linters caught this.  Update to be
more correct.

Change-Id: I95f34611ef5733e930eead1cbe5ee4573ea7aadf
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/project-config,openstack-infra/project-config