### 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_
keys = set()
    for tag in tag_set:
        if set(tag) != {"Key", "Value"}:
            raise MalformedXML()
        key = tag["Key"]
        if key in keys:
            raise InvalidTag(
                "Cannot provide multiple Tags with the same key",
                TagKey=key,
            )
        if key.startswith("aws:"):
            if type_set == "bucket":
                message = "System tags cannot be added/updated by requester"
            else:
                message = "Your TagKey cannot be prefixed with aws:"
            raise InvalidTag(
                message,
                TagKey=key,
            )
        if not TAG_REGEX.match(key):
            raise InvalidTag(
                "The TagKey you have provided is invalid",
                TagKey=key,
            )
        elif not TAG_REGEX.match(tag["Value"]):
            raise InvalidTag(
                "The TagValue you have provided is invalid", TagKey=key, TagValue=tag["Value"]
            )
        keys.add(key)
def get_unique_key_id(