BCI-3620 Fix TestIntegration_KeeperPluginLogUpkeep_ErrHandler flaky test

[dhaidashenko]

Fix guarantee that the block, used as a start filter in query to verify that event is present on chain, was actually committed before event.

[cl-sonarqube-production[bot]]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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