Fix install mode compatibility checking

[joelanford]

When the operator group exists and has a single target namespace, there are actually still three possible supported install modes:

• When the target namespace is "", that means all namespaces
• When the target namespace == og.metadata.namespace, that means own namespace
• Otherwise, that means single namespace

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: joelanford

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/operator-framework/kubectl-operator/blob/main/OWNERS)~~ [joelanford] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[exdx]

/lgtm