r/aws_ecs_service: fix crash from nil service_registries item

[jar-b]

Description

This appears only to be possible with dynamic blocks as explicitly setting a nil service_registries block will prompt for the required attributes within the block. However, this fix should prevent the nil value from being expanded and causing a crash under the dynamic block scenario.

Relations

Closes #34166

References

Output from Acceptance Testing

% make testacc PKG=ecs TESTS=TestAccECSService_ServiceRegistries
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.22.6 test ./internal/service/ecs/... -v -count 1 -parallel 20 -run='TestAccECSService_ServiceRegistries'  -timeout 360m

--- PASS: TestAccECSService_ServiceRegistries_basic (145.59s)
--- PASS: TestAccECSService_ServiceRegistries_container (145.60s)
--- PASS: TestAccECSService_ServiceRegistries_removal (156.46s)
--- PASS: TestAccECSService_ServiceRegistries_changes (279.51s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/ecs        285.700s

[github-actions]

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[ewbankkit]

LGTM 🚀.

[github-actions]

This functionality has been released in v5.63.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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