Fix nightly images getting timestamp/git hash (#493)

Author: sjpb

.github/workflows/nightlybuild.yml

@@ -83,6 +83,7 @@ jobs:
           -var-file=$PKR_VAR_environment_root/${{ env.CI_CLOUD }}.pkrvars.hcl \
           -var "source_image_name=${{ matrix.build.source_image_name }}" \
           -var "image_name=${{ matrix.build.image_name }}" \
+          -var "image_name_version="\
           -var "inventory_groups=${{ matrix.build.inventory_groups }}" \
           openstack.pkr.hcl