test: Ignore World Scientific journal URLs during Sphinx linkcheck (#…

…2308)

* Ignore URLs for World Scientific journal article
 https://doi.org/10.1142/S0217732321020016 from Sphinx linkcheck tests.

 Avoids:

```
403 Client Error: Forbidden for url:
https://www.worldscientific.com/doi/abs/10.1142/S0217732321020016
```

docs/conf.py

@@ -519,6 +519,8 @@ def setup(app):
     r'https://indico.desy.de/event/22731/.*',
     # https://indico.belle2.org/event/8470/contributions/55871/ is frequently generating 403 Client Error
     r'https://indico.belle2.org/event/8470/.*',
+    # https://doi.org/10.1142/S0217732321020016 is frequently generating 403 Client Error
+    r'https://doi\.org/10.1142/.*',
     # CERN doesn't maintain its SSL certs well enough to not have SSLErrors
     r'https://twiki.cern.ch/.*',
     # tags for a release won't exist until it is made, but the release notes