tests/operator/operator.go: Replace `Update()` with `Patch()`

[orenc1]

Replace Update() with Patch() operation in order to mitigate conflicts on updating the Kubevirt resource at the test VirtualMachineInstancesPerNode test case at tests/operator/operator.go

What this PR does

Before this PR:

After this PR:

Fixes # Jira-ticket: https://issues.redhat.com/browse/CNV-45287

Why we need it and why it was done in this way

The following tradeoffs were made:

The following alternatives were considered:

Links to places where the discussion took place:

Special notes for your reviewer

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR. Approvers are expected to review this list.

• [ ] Design: A design document was considered and is present (link) or not required
• [ ] PR: The PR description is expressive enough and will help future contributors
• [ ] Code: Write code that humans can understand and Keep it simple
• [ ] Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• [ ] Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• [ ] Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• [ ] Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• [ ] Community: Announcement to kubevirt-dev was considered

Release note

replace `Update()` with `Patch()` for `test VirtualMachineInstancesPerNode`