microshift-olm is missing openshift-marketplace namespace which is sort of a global namespace that allows operators to be created in other namespaces if the CatalogSource resides in it

1. Create CatalogSource
2. Create Subscription in openshift-operators namespace and reference CatalogSource's namespace in the `sourceNamespace` field

CatalogSource is created in openshift-operator-lifecycle-manager namespace:

Subscription in openshift-operators namespace with sourceNamespace: openshift-operator-lifecycle-manager is not handled because (from its Status):
constraints not satisfiable: no operators found from catalog operatorhubio-catalog in namespace openshift-operator-lifecycle-manager referenced by subscription my-cert-manager, subscription my-cert-manager exists

CatalogSource is created in openshift-marketplace namespace:

Subscription in openshift-operators namespace with sourceNamespace: openshift-marketplace is handled correctly and the requested operator is created in openshift-operators namespace

This behavior is caused by configuration of the catalog operator, namely the --namespace openshift-marketplace option:
https://github.com/openshift/microshift/blob/1c18ad89d7559f1ee65f64145592de84d6ff7a57/assets/optional/operator-lifecycle-manager/0000_50_olm_08-catalog-operator.deployment.yaml#L53-L54