### 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_
bucket = s3_create_bucket()
        key = "en-gb.wav"
        file_path = os.path.join(os.path.dirname(__file__), f"../../files/{key}")
        aws_client.s3.upload_file(file_path, bucket, key)
        s = aws_client.s3.list_s(Bucket=bucket)
        etag = s["Contents"][0]["ETag"]
        # TODO
        with pytest.raises(ClientError) as e:
            aws_client.s3.get_(Bucket=bucket, Key=key, IfNoneMatch=etag)
        snapshot.match("if_none_match_err_1", e.value.response["Error"])
        with pytest.raises(ClientError) as e:
            aws_client.s3.get_(Bucket=bucket, Key=key, IfNoneMatch=etag.strip('"'))
        snapshot.match("if_none_match_err_2", e.value.response["Error"])
        response = aws_client.s3.get_(Bucket=bucket, Key=key, IfNoneMatch="etag")
        snapshot.match("if_none_match_1", response["ResponseMetadata"]["HTTPStatusCode"])
        response = aws_client.s3.get_(Bucket=bucket, Key=key, IfMatch=etag)
        snapshot.match("if_match_1", response["ResponseMetadata"]["HTTPStatusCode"])
        response = aws_client.s3.get_(Bucket=bucket, Key=key, IfMatch=etag.strip('"'))
        snapshot.match("if_match_2", response["ResponseMetadata"]["HTTPStatusCode"])
        with pytest.raises(ClientError) as e:
            aws_client.s3.get_(Bucket=bucket, Key=key, IfMatch="etag")
        snapshot.match("if_match_err_1", e.value.response["Error"])
    @markers.aws.validated
    def test_s3_inventory_report_crud(self, aws_client, s3_create_bucket, snapshot):