### 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_
aws_client.s3.put_(Bucket=s3_bucket, Key=key_name, Body="This body document")
            delete_.append({"Key": key_name})
        response = aws_client.s3.delete_s(Bucket=s3_bucket, Delete={"s": delete_})
        snapshot.match("batch-delete", response)
        response = aws_client.s3.list_s(Bucket=s3_bucket)
        snapshot.match("list-remaining-s", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_s3_get__header_overrides(self, s3_bucket, snapshot, aws_client):
        # Sign
        # http
        _key = "key-header-overrides"
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Body="something")
        expiry_date = "Wed, 21 Oct 2015 07:28:00 GMT"
        response = aws_client.s3.get_(
            Bucket=s3_bucket,
            Key=_key,
            ResponseCacheControl="max-age=74",
            ResponseContentDisposition='attachment; filename="foo.jpg"',
            ResponseContentEncoding="identity",
            ResponseContentLanguage="de-DE",
            ResponseContentType="image/jpeg",
            ResponseExpires=expiry_date,
        )
        snapshot.match("get-", response)
    @markers.aws.only_localstack
    def test_virtual_host_proxying_headers(self, s3_bucket, aws_client):