### 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.match("head--ver2", head_)
        # remo
        resp = aws_client.s3.put__legal_hold(
            Bucket=bucket_name,
            Key=_key,
            VersionId=version_id,
            LegalHold={"Status": "OFF"},
        )
        snapshot.match("remove--legal-hold-ver1", resp)
        head_ = aws_client.s3.head_(
            Bucket=bucket_name, Key=_key, VersionId=version_id
        )
        snapshot.match("head--ver1-no-lock", head_)
        # now 
        resp = aws_client.s3.delete_(
            Bucket=bucket_name,
            Key=_key,
            VersionId=version_id,
        )
        snapshot.match("delete--ver1", resp)
        # disa
        aws_client.s3.put__legal_hold(
            Bucket=bucket_name,
            Key=_key,
            LegalHold={"Status": "OFF"},
            VersionId=version_id_2,
        )
    @markers.aws.validated
    def test_s3_copy__legal_hold(self, s3_create_bucket, snapshot, aws_client):