Fix CO-DETR load_from url in config

[returnL]

Motivation

Training the CO-DETR model resulted in an error like #11167

Modification

The URL in config is inaccessible, replace it with the URL in the README

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMPreTrain.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.