Add scos tag to machine-config-operator images when building on OKD f…

…or (#51422)

scos

Avoid the below error when building a release image for OKD:

```
operator "machine-config-operator" contained an invalid image-references file: no input image tag named "rhel-coreos"
```

ci-operator/config/openshift/machine-config-operator/openshift-machine-config-operator-master__okd-scos.yaml

@@ -17,7 +17,10 @@ build_root:
     namespace: ocp
     tag: rhel-8-golang-1.21-openshift-4.16
 images:
-- dockerfile_path: Dockerfile.rhel7
+- build_args:
+  - name: TAGS
+    value: scos
+  dockerfile_path: Dockerfile.rhel7
   from: origin_scos-4.16_base-stream9
   inputs:
     ocp_builder_rhel-8-golang-1.21-openshift-4.16: