Run Markdownlint in CI instead of having its code in the repository

Author: Salamandar

.github/workflows/markdownlint.yml

@@ -0,0 +1,19 @@
+name: Lint Markdown
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - uses: DavidAnson/markdownlint-cli2-action@v19
+      with:
+        config: .markdownlint.json
+        globs: '**/*.md'

.markdownlint.json

@@ -1,5 +1,4 @@
 {
-    "extends": "markdownlint-rules-grav-pages/rules/frontmatter.schema.json",
     "default": true,
     "code-block-style": {
         "style": "fenced"
@@ -61,4 +60,4 @@
     "line-length": false,
     "no-reversed-links": false,
     "no-missing-space-atx": false
-}
+}