fix: restore CI for Traefik v1.7

Co-authored-by: Michael <michael.matur@gmail.com>

.github/workflows/check_doc.yaml

@@ -0,0 +1,21 @@
+name: Check Documentation
+
+on:
+  pull_request:
+    branches:
+      - '*'
+
+jobs:
+
+  docs:
+    name: Check, verify and build documentation
+    runs-on: ubuntu-20.04
+
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - name: Check documentation
+        run: make docs-verify