[data_source_datadog_service_account] acc test: reproduce service account datasource bug on exact match filter

[pablito-perez]

Reproduces the behaviour described in #2571

TL;DR exact_match filter on service_account might be incorrect when the API returns multiple items

[pablito-perez]

• #2572
• #2574 👈 (View in Graphite)
• master

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[ecdatadog]

Thanks to the change of behavior of pointers in loops (https://go.dev/blog/loopvar-preview) in Go 1.22, this issue has been solved at langage level !