### 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_
try:
        parsed_tags = urlparser.parse_qs(tagging_header, keep_blank_values=True)
        tags: dict[str, str] = {}
        for key, val in parsed_tags.items():
            if len(val) != 1 or not TAG_REGEX.match(key) or not TAG_REGEX.match(val[0]):
                raise InvalidArgument(
                    "The header 'x-amz-tagging' shall be encoded as UTF-8 then URLEncoded URL query parameters without tag name duplicates.",
                    ArgumentName="x-amz-tagging",
                    ArgumentValue=tagging_header,
                )
            elif key.startswith("aws:"):
                raise
            tags[key] = val[0]
        return tags
    except ValueError:
        raise InvalidArgument(
            "The header 'x-amz-tagging' shall be encoded as UTF-8 then URLEncoded URL query parameters without tag name duplicates.",
            ArgumentName="x-amz-tagging",
            ArgumentValue=tagging_header,
        )
def validate_tag_set(tag_set: TagSet, type_set: Literal["bucket", "object"] = "bucket"):