Fix sphinx docs linting

.github/sphinx-problem-matcher.json

@@ -0,0 +1,15 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "sphinx",
+      "pattern": [
+        {
+          "regexp": "^([^:]+):(\\d+): (WARNING: )?(.+)$",
+          "file": 1,
+          "line": 2,
+          "message": 4
+        }
+      ]
+    }
+  ]
+}

.github/workflows/lint.yml

@@ -118,7 +118,11 @@ jobs:
       - name: Install dependencies
         run: poetry install --only=docs
 
-      - uses: sphinx-doc/github-problem-matcher@master
-        name: Build docs
-        with:
-          run: poe docs
+      - name: Add Sphinx problem matcher
+        run: echo "::add-matcher::.github/sphinx-problem-matcher.json"
+
+      - name: Build docs
+        run: |
+          poe docs |& tee /tmp/output
+          # fail the job if there are issues
+          grep -q " WARNING:" /tmp/output && exit 1 || exit 0