AthenaPoolExampleAlgorithms: ensure we always have xAOD::EventInfo when needed

Tadej Novakrequested to merge
tadej/athena:eventtag/example into master

AthenaPoolExampleAlgorithms: ensure we always have xAOD::EventInfo when needed to write event tag. This will test the default workflow.

Related to ATEAM-643.

/cc @gemmeren @ssnyder

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