### 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.add_transformer(snapshot.transform.s3_api())
        dest_bucket = s3_create_bucket()
        special_keys = [
            "file%2Fname",
            "test@key/",
            "test key/",
            "test key//",
            "a/%F0%9F%98%80/",
            "test+key",
        ]
        for key in special_keys:
            resp = aws_client.s3.put_(Bucket=s3_bucket, Key=key, Body=b"test")
            snapshot.match(f"put--src-special-char-{key}", resp)
            copy_obj = aws_client.s3.copy_(
                Bucket=dest_bucket,
                Key=key,
                CopySource=f"{s3_bucket}/{key}",
            )
            snapshot.match(f"copy--special-char-{key}", copy_obj)
        resp = aws_client.s3.list_s_v2(Bucket=dest_bucket)
        snapshot.match("list--copy-dest-special-char", resp)
    @markers.aws.validated
    @pytest.mark.skipif(
        condition=LEGACY_V2_S3_PROVIDER, reason="moto does not handle this edge case"
    )
    def test_copy__special_character_plus_for_space(