test/aws_dynamodb_global_table: Use single region for basic and import testing

[bflad]

Due to limitations with the import process, this fails in acceptance testing when there are multiple regions involved:

=== RUN   TestAccAwsDynamoDbGlobalTable_import
--- FAIL: TestAccAwsDynamoDbGlobalTable_import (34.04s)
    testing.go:573: Error destroying resource! WARNING: Dangling resources
        may exist. The full state and error is shown below.
        
        Error: config is invalid: aws_dynamodb_global_table.test: configuration for provider.aws.us-east-1 is not present; a provider configuration block is required for all operations

Basic/import testing should have been one region anyways. My bad. 🤕

Passing for me locally and I'll run it in TeamCity.

make testacc TEST=./aws TESTARGS='-run=TestAccAwsDynamoDbGlobalTable'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAwsDynamoDbGlobalTable -timeout 120m
=== RUN   TestAccAwsDynamoDbGlobalTable_basic
--- PASS: TestAccAwsDynamoDbGlobalTable_basic (87.11s)
=== RUN   TestAccAwsDynamoDbGlobalTable_multipleRegions
--- PASS: TestAccAwsDynamoDbGlobalTable_multipleRegions (104.13s)
=== RUN   TestAccAwsDynamoDbGlobalTable_import
--- PASS: TestAccAwsDynamoDbGlobalTable_import (85.84s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	277.125s

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!