docs(backport): Update docs build requirements

* Backport components of:
   - PR https://github.com/scikit-hep/pyhf/pull/ 2252
   - PR https://github.com/scikit-hep/pyhf/pull/ 2255
   - PR https://github.com/scikit-hep/pyhf/pull/ 2267
   - PR https://github.com/scikit-hep/pyhf/pull/ 2271
   - PR https://github.com/scikit-hep/pyhf/pull/ 2272
   - PR https://github.com/scikit-hep/pyhf/pull/ 2276

docs/conf.py

@@ -515,6 +515,12 @@ def setup(app):
     r'https://doi\.org/10\.31526/.*',
     # https://doi.org/10.1051/epjconf/x DOI URLs will periodically generate 500 Server Error
     r'https://doi\.org/10\.1051/epjconf/.*',
+    # https://indico.desy.de/event/22731/contributions/47953/ is frequently generating 403 Client Error
+    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/.*',
+    # 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
     # and ReadTheDocs need to reference them
     r'https://github.com/scikit-hep/pyhf/releases/tag/.*',