### 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_
:raises NotModified, 304 with an empty body
    """
    precondition_failed = None
    
    last_modified = last_modified.replace(microsecond=0)
    if (if_match := request.get("IfMatch")) and etag != if_match.strip('"'):
        precondition_failed = "If-Match"
    elif (
        if_unmodified_since := request.get("IfUnmodifiedSince")
    ) and last_modified > if_unmodified_since:
        precondition_failed = "If-Unmodified-Since"
    if precondition_failed:
        raise PreconditionFailed(
            "At least one of the pre-conditions you specified did not hold",
            Condition=precondition_failed,
        )
    if ((if_none_match := request.get("IfNoneMatch")) and etag == if_none_match.strip('"')) or (
        (if_modified_since := request.get("IfModifiedSince"))
        and last_modified <= if_modified_since < datetime.datetime.now(tz=_gmt_zone_info)
    ):
        raise CommonServiceException(
            message="Not Modified",
            code="NotModified",
            status_code=304,
        )
def get_canned_acl(
    canned_acl: BucketCannedACL | ObjectCannedACL, owner: Owner
) -> AccessControlPolicy:
    """
    Return the proper Owner and Grants from a CannedACL