### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
response = client_1.get_bucket_location(Bucket=bucket_1_name)
        snapshot.match("get_bucket_location_bucket_1", response)
        region_2 = "us-east-2"
        client_2 = aws_client_factory(region_name=region_2).s3
        bucket_2_name = f"bucket-{short_uid()}"
        s3_create_bucket_with_client(
            client_2,
            Bucket=bucket_2_name,
            CreateBucketConfiguration={"LocationConstraint": region_2},
        )
        response = client_2.get_bucket_location(Bucket=bucket_2_name)
        snapshot.match("get_bucket_location_bucket_2", response)
        # asse
        with pytest.raises(Exception) as exc:
            client_2.create_bucket(Bucket=f"bucket-{short_uid()}")
        snapshot.match("create_bucket_constraint_exc", exc.value.response)
        bucket_3_name = f"bucket-{short_uid()}"
        response = s3_create_bucket_with_client(
            client_2,
            Bucket=bucket_3_name,
            CreateBucketConfiguration={"LocationConstraint": region_2},
        )
        snapshot.match("create_bucket_bucket_3", response)
        response = client_2.get_bucket_location(Bucket=bucket_3_name)
        snapshot.match("get_bucket_location_bucket_3", response)
        with pytest.raises(ClientError) as exc:
            aws_client.s3.get_bucket_location(Bucket=f"random-bucket-test-{short_uid()}")
        snapshot.match("get_bucket_location_non_existent_bucket", exc.value.response)
    @markers.aws.validated
    def test_bucket_operation_between_regions(