GitHub Actions: Add json problem matcher

.github/workflows/ci.yaml

@@ -387,6 +387,9 @@ jobs:
         run: |
           echo "Failed to restore Python virtual environment from cache"
           exit 1
+      - name: Register check-json problem matcher
+        run: |
+          echo "::add-matcher::.github/workflows/matchers/check-json.json"
       - name: Run check-json
         run: |
           . venv/bin/activate

.github/workflows/matchers/check-json.json

@@ -0,0 +1,16 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "check-json",
+      "pattern": [
+        {
+          "regexp": "^(.+):\\s(.+\\sline\\s(\\d+)\\scolumn\\s(\\d+).+)$",
+          "file": 1,
+          "message": 2,
+          "line": 3,
+          "column": 4
+        }
+      ]
+    }
+  ]
+}