Add autodoc warnings to the problem matcher.

This should enable us to at least flag autodoc
import errors in the diff view.
Catching error otherwise is not feasible, see pymeasure#583.

.github/sphinx.json

@@ -21,6 +21,18 @@
                     "message": 3
                 }
             ]
+        },
+        {
+            "owner": "sphinx-extension",
+            "file": "docs/conf.py",
+            "pattern": [
+                {
+                    "regexp": "^(?<severity>WARNING|ERROR): (?<code>\\S+): (?<message>.+)$",
+                    "severity": 1,
+                    "code": 2,
+                    "message": 3
+                }
+            ]
         }
     ]
 }