Add verification polling to service account updates

[chasevedder]

Recently there has been some flakiness is service account tests involving updates. These test failures are the result of updates not being propagated by the time validation is done. There is already a 5 second sleep, but in order to make the results more consistent this fix applies polling to check for field updates before considering the update a success. This is similar to the fix in #14547 for creates. Unlike creates however, this does not result in inconsistent state for the terraform resource, so it largely only affects tests.

resourcemanager: added verification polling to service account updates to ensure the resource is consistent before succeeding

[github-actions]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit bea16f9:

Diff report

Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
google provider	View Diff	1 file changed, 76 insertions(+), 14 deletions(-)
google-beta provider	View Diff	1 file changed, 76 insertions(+), 14 deletions(-)

Test report

Analytics

Total Tests	Passed	Skipped	Affected
173	142	30	1

Affected Service Packages

• resourcemanager

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Step 1: Replaying Mode

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccServiceAccount_basic

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Step 2: Recording Mode

Recording Mode	Replaying Rerun	Test Name
✅ Log	✅	TestAccServiceAccount_basic

🟢 All tests passed!

View the build log or the debug logs folder for detailed results.

@chasevedder, @slevenick VCR tests complete for bea16f9!