tests/resource/aws_cloudtrail: fix testAccAWSCloudTrail_cloudwatch (#14762)
tests/resource/aws_cloudtrail: fix testAccAWSCloudTrail_cloudwatch (#14762)

Output from acceptance testing:

```
--- PASS: TestAccAWSCloudTrail_serial (314.43s)
    --- PASS: TestAccAWSCloudTrail_serial/Trail (314.43s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/tags (38.95s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/eventSelector (71.74s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/cloudwatch (45.68s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/includeGlobalServiceEvents (15.43s)
        --- SKIP: TestAccAWSCloudTrail_serial/Trail/isOrganization (1.01s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/logValidation (26.69s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/basic (26.08s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/enableLogging (36.95s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/isMultiRegion (36.16s)
        --- PASS: TestAccAWSCloudTrail_serial/Trail/kmsKey (15.73s)
```
terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws