GitHub Actions: Add yamllint problem matcher

.github/workflows/ci.yaml

@@ -486,6 +486,9 @@ jobs:
         run: |
           echo "Failed to restore Python virtual environment from cache"
           exit 1
+      - name: Register yamllint problem matcher
+        run: |
+          echo "::add-matcher::.github/workflows/matchers/yamllint.json"
       - name: Run yamllint
         run: |
           . venv/bin/activate

.github/workflows/matchers/yamllint.json

@@ -0,0 +1,22 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "yamllint",
+      "pattern": [
+        {
+          "regexp": "^(.*\\.ya?ml)$",
+          "file": 1
+        },
+        {
+          "regexp": "^\\s{2}(\\d+):(\\d+)\\s+(error|warning)\\s+(.*?)\\s+\\((.*)\\)$",
+          "line": 1,
+          "column": 2,
+          "severity": 3,
+          "message": 4,
+          "code": 5,
+          "loop": true
+        }
+      ]
+    }
+  ]
+}