test: Ignore EPJ Web of Conferences DOI URLs during Sphinx linkcheck (#…

…1870)

* Ignore DOI URLs for EPJ Web of Conferences from Sphinx linkcheck tests as the DOI
URLs will periodically fail to resolve given '500 Server Error' as the result of
EPJ backend problems.

docs/conf.py

@@ -468,5 +468,7 @@ def setup(app):
     'cli.html#pyhf-xml2json',
     # https://doi.org/10.31526/lhep.2020.158 is causing linkcheck connection timeouts in CI
     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/.*',
 ]
 linkcheck_retries = 50