Fix guaranteed bucket logs tests

[sagihirshfeld]

A small fix to ocs-ci/tests/functional/object/mcg/test_bucket_logs.py::TestBucketLogs::test_bucket_logs_integrity:

• Fix the use of append to add on the expected_ops_set at BucketLoggingManager:verify_logs_integrity
• Update the expectation for incoming logs to start with a forward-slash at test_bucket_logs_integrity

[ocs-ci]

PR validation on existing cluster

Cluster Name: shirshfe-417ibm42
Cluster Configuration:
PR Test Suite:
PR Test Path: tests/functional/object/mcg/test_bucket_logs.py
Additional Test Params:
OCP VERSION: 4.17
OCS VERSION: 4.17
tested against branch: master

Job PASSED.

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: DanielOsypenko, sagihirshfeld, udaysk23

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