### 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_
Key="data.txt",
            Attributes=["StorageClass", "ETag", "Size", "Parts", "Checksum"],
        )
        snapshot.match("-attrs", response)
        multipart_key = "test-get-obj-attrs-multipart"
        s3_multipart_upload(bucket=s3_bucket, key=multipart_key, data="upload-part-1" * 5)
        response = aws_client.s3.get__attributes(
            Bucket=s3_bucket,
            Key=multipart_key,
            Attributes=["StorageClass", "ETag", "Size", "Parts"],
        )
        snapshot.match("-attrs-multiparts-1-part", response)
        multipart_key = "test-get-obj-attrs-multipart-2"
        s3_multipart_upload(bucket=s3_bucket, key=multipart_key, data="upload-part-1" * 5, parts=2)
        response = aws_client.s3.get__attributes(
            Bucket=s3_bucket,
            Key=multipart_key,
            Attributes=["StorageClass", "ETag", "Size", "Parts"],
            MaxParts=3,
        )
        snapshot.match("-attrs-multiparts-2-parts", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=[
            "$..ServerSideEncryption",
            "$..DeleteMarker",
        ],
    )
    def test_get__attributes_versioned(self, s3_bucket, snapshot, aws_client):