### 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_
"""Boto adds a trailing slash always?"""
        snapshot.add_transformer(snapshot.transform.key_value("Name"))
        s3_config = {"addressing_s": "virtual"} if use_virtual_address else {}
        s3_client = aws_client_factory(
            config=Config(s3=s3_config),
            endpoint_url=_endpoint_url(),
        ).s3
        key = "test@key/"
        s3_client.put_(Bucket=s3_bucket, Key=key, Body=b"test-non-encoded")
        encoded_key = "test%40key/"
        s3_client.put_(Bucket=s3_bucket, Key=encoded_key, Body=b"test-encoded")
        encoded_key_no_trailing = "test%40key"
        s3_client.put_(
            Bucket=s3_bucket, Key=encoded_key_no_trailing, Body=b"test-encoded-no-trailing"
        )
        # as
        assert s3_client.get_(Bucket=s3_bucket, Key=key)["Body"].read() == b"test-non-encoded"
        assert (
            s3_client.get_(Bucket=s3_bucket, Key=encoded_key)["Body"].read()
            == b"test-encoded"
        )
        assert (
            s3_client.get_(Bucket=s3_bucket, Key=encoded_key_no_trailing)["Body"].read()
            == b"test-encoded-no-trailing"
        )
        resp = s3_client.list_s_v2(Bucket=s3_bucket)
        snapshot.match("list--encoded-char", resp)
    @markers.aws.validated
    def test_get__no_such_bucket(self, snapshot, aws_client):