test: improve SearchOperationsTest postgres coverage

[msmithstubbs]

Implement feedback on test improvements from #3307

• use `TestUtils.setup_single_tenant' macro
• remove unnecessary mocks
• stub exception for postgres error

[amokan]

Hey @msmithstubbs 👋

The test changes look good. My only concern is the addition of the rescue block in search operations - which does change production behavior a bit.

If there is a need to include the rescue block, could we at least tighten that up to only rescue Postgrex.Error?

[msmithstubbs]

The test changes look good. My only concern is the addition of the rescue block in search operations - which does change production behavior a bit.

If there is a need to include the rescue block, could we at least tighten that up to only rescue Postgrex.Error?

Yeah, you're right: we don't need it. I've removed it and updated the test to assert any exceptions are passed through.

Might be worth considering rescuing some exceptions to align the Postgres code path closer to BigQuery but that should be a separate PR.