Made unused async fields optional

[melinath]

Resolved hashicorp/terraform-provider-google#14976

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

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

Diff report

Your PR hasn't generated any diffs, but I'll let you know if a future commit does.

[modular-magician]

Tests analytics

Total tests: 2853
Passed tests 2550
Skipped tests: 297
Affected tests: 6

Action taken

Found 6 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccPubsubSubscriptionIamPolicy|TestAccContainerAwsNodePool_BetaBasicHandWritten|TestAccComputeFirewallPolicyRule_multipleRules|TestAccVertexAIIndex_updated|TestAccVertexAIIndex_vertexAiIndexStreamingExample|TestAccVertexAIIndex_vertexAiIndexExample

Get to know how VCR tests work

[modular-magician]

$\textcolor{green}{\textsf{Tests passed during RECORDING mode:}}$
TestAccPubsubSubscriptionIamPolicy[Debug log]

Rerun these tests in REPLAYING mode to catch issues

$\textcolor{green}{\textsf{No issues found for passed tests after REPLAYING rerun.}}$

---

$\textcolor{red}{\textsf{Tests failed during RECORDING mode:}}$
TestAccContainerAwsNodePool_BetaBasicHandWritten[Error message] [Debug log]
TestAccComputeFirewallPolicyRule_multipleRules[Error message] [Debug log]
TestAccVertexAIIndex_updated[Error message] [Debug log]
TestAccVertexAIIndex_vertexAiIndexStreamingExample[Error message] [Debug log]
TestAccVertexAIIndex_vertexAiIndexExample[Error message] [Debug log]

$\textcolor{red}{\textsf{Please fix these to complete your PR.}}$
View the build log or the debug log for each test

[melinath]

@rileykarson could you take a look at this PR?