### 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_
Attributes=["StorageClass", "ETag", "Size"],
        )
        snapshot.match("get--attrs-v1", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    @markers.snapshot.skip_snapshot_verify(paths=["$..NextKeyMarker", "$..NextUploadIdMarker"])
    def test_multipart_and_list_parts(self, s3_bucket, snapshot, aws_client):
        snapshot.add_transformer(
            [
                snapshot.transform.key_value("Bucket", reference_replacement=False),
                snapshot.transform.key_value("DisplayName", reference_replacement=False),
                snapshot.transform.key_value("UploadId"),
                snapshot.transform.key_value("Location"),
                snapshot.transform.key_value(
                    "ID", value_replacement="owner-id", reference_replacement=False
                ),
            ]
        )
        key_name = "test-list-parts"
        response = aws_client.s3.create_multipart_upload(Bucket=s3_bucket, Key=key_name)
        snapshot.match("create-multipart", response)
        upload_id = response["UploadId"]
        list_part = aws_client.s3.list_parts(Bucket=s3_bucket, Key=key_name, UploadId=upload_id)
        snapshot.match("list-part-after-created", list_part)
        list_multipart_uploads = aws_client.s3.list_multipart_uploads(Bucket=s3_bucket)
        snapshot.match("list-all-uploads", list_multipart_uploads)