Onetime scan fix

[XianJiChen]

dataplex: fixed acceptance test failure for one time scans

this pr is to fix hashicorp/terraform-provider-google#26716
The tests were failing/flaky because one time datascan triggers a datascan job run right after creation, and since examples scans have trivial setup so the job run could be quick, and therefore, when the pipeline performs import test, it will see the execution_status.0.latest_job_end_time being populated which leads to mismatch.
In this pr we also removed the used of redundant ignore_read_extra for dataplex_datascan_execution_identity_service_account as it uses an on_demand trigger which won't trigger a new scan job.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 1 file changed, 3 insertions(+), 3 deletions(-))
google-beta provider: Diff ( 1 file changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 83
Passed tests: 83
Skipped tests: 0
Affected tests: 0

Click here to see the affected service packages

• dataplex

🟢 All tests passed!

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[github-actions]

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