### 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_
snapshot.add_transformer(snapshot.transform.s3_api())
        response = aws_client.s3.put_(Bucket=s3_bucket, Key="Ā0Ä", Body=b"abc123")
        assert response["ResponseMetadata"]["HTTPStatusCode"] == 200
        snapshot.match("put-", response)
        response = aws_client.s3.get_(Bucket=s3_bucket, Key="Ā0Ä")
        snapshot.match("get-", response)
        assert response["Body"].read() == b"abc123"
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(paths=["$..MaxAttemptsReached"])
    @markers.snapshot.skip_snapshot_verify(
        paths=[
            "$..HTTPHeaders.connection",
            # TO
            "$..HTTPHeaders.content-length",  # 58
            "$..HTTPHeaders.content-type",  # ap
        ],
    )  # fo
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=[
            "$..HTTPHeaders.x-amz-server-side-encryption",
            "$..ServerSideEncryption",
        ],
    )
    def test_put_and_get__with_content_language_disposition(