Fix `internal.percona.com/delete-backup` finalizer

[pooknull]

CHANGE DESCRIPTION

Problem: Short explanation of the problem.

Cause: Short explanation of the root cause of the issue if applicable.

Solution: Short explanation of the solution we are providing with this PR.

CHECKLIST

Jira

• [ ] Is the Jira ticket created and referenced properly?
• [ ] Does the Jira ticket have the proper statuses for documentation (Needs Doc) and QA (Needs QA)?
• [ ] Does the Jira ticket link to the proper milestone (Fix Version field)?

Tests

• [ ] Is an E2E test/test case added for the new feature/change?
• [ ] Are unit tests added where appropriate?

Config/Logging/Testability

• [ ] Are all needed new/changed options added to default YAML files?
• [ ] Are all needed new/changed options added to the Helm Chart?
• [ ] Did we add proper logging messages for operator actions?
• [ ] Did we ensure compatibility with the previous version or cluster upgrade process?
• [ ] Does the change support oldest and newest supported PG version?
• [ ] Does the change support oldest and newest supported Kubernetes version?