Add 'TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy'.

Acceptance test output:

% make testacc TESTARGS='-run=TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy' PKG=s3
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.23.5 test ./internal/service/s3/... -v -count 1 -parallel 20  -run=TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy -timeout 360m -vet=off
2025/02/27 11:10:55 Initializing Terraform AWS Provider...
=== RUN   TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy
=== PAUSE TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy
=== CONT  TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy
--- PASS: TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy (51.84s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/s3	57.463s

internal/service/s3/directory_bucket_test.go

@@ -177,6 +177,50 @@ func TestAccS3DirectoryBucket_defaultDataRedundancy(t *testing.T) {
 	})
 }
 
+func TestAccS3DirectoryBucket_upgradeDefaultDataRedundancy(t *testing.T) {
+	ctx := acctest.Context(t)
+	rName := sdkacctest.RandomWithPrefix(acctest.ResourcePrefix)
+	resourceName := "aws_s3_directory_bucket.test"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:     func() { acctest.PreCheck(ctx, t) },
+		ErrorCheck:   acctest.ErrorCheck(t, names.S3ServiceID),
+		CheckDestroy: testAccCheckDirectoryBucketDestroy(ctx),
+		Steps: []resource.TestStep{
+			{
+				ExternalProviders: map[string]resource.ExternalProvider{
+					"aws": {
+						Source:            "hashicorp/aws",
+						VersionConstraint: "5.88.0",
+					},
+				},
+				Config: testAccDirectoryBucketConfig_basic(rName),
+				Check: resource.ComposeAggregateTestCheckFunc(
+					testAccCheckDirectoryBucketExists(ctx, resourceName),
+				),
+				ConfigPlanChecks: resource.ConfigPlanChecks{
+					PreApply: []plancheck.PlanCheck{
+						plancheck.ExpectResourceAction(resourceName, plancheck.ResourceActionCreate),
+						plancheck.ExpectKnownValue(resourceName, tfjsonpath.New("data_redundancy"), knownvalue.StringExact("SingleAvailabilityZone")),
+					},
+				},
+			},
+			{
+				ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories,
+				Config:                   testAccDirectoryBucketConfig_basic(rName),
+				Check: resource.ComposeAggregateTestCheckFunc(
+					testAccCheckDirectoryBucketExists(ctx, resourceName),
+				),
+				ConfigPlanChecks: resource.ConfigPlanChecks{
+					PreApply: []plancheck.PlanCheck{
+						plancheck.ExpectResourceAction(resourceName, plancheck.ResourceActionNoop),
+					},
+				},
+			},
+		},
+	})
+}
+
 func testAccCheckDirectoryBucketDestroy(ctx context.Context) resource.TestCheckFunc {
 	return func(s *terraform.State) error {
 		conn := acctest.Provider.Meta().(*conns.AWSClient).S3ExpressClient(ctx)