### 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=bucket_name,
            WebsiteConfiguration={
                "IndexDocument": {"Suffix": "index.html"},
            },
        )
        snapshot.match("put-website-config-region-1", put_website_config)
        bucket_cors_config = {
            "CORSRules": [
                {
                    "AllowedOrigins": ["*"],
                    "AllowedMethods": ["GET"],
                }
            ]
        }
        put_cors_config = client_1.put_bucket_cors(
            Bucket=bucket_name, CORSConfiguration=bucket_cors_config
        )
        snapshot.match("put-cors-config-region-1", put_cors_config)
        region_2 = "us-east-1"
        client_2 = aws_client_factory(region_name=region_2).s3
        get_website_config = client_2.get_bucket_website(Bucket=bucket_name)
        snapshot.match("get-website-config-region-2", get_website_config)
        get_cors_config = client_2.get_bucket_cors(Bucket=bucket_name)
        snapshot.match("get-cors-config-region-2", get_cors_config)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_get__with_anon_credentials(