fix(ci): use act_runner

.gitea/workflows/markdown-linters.yaml

@@ -0,0 +1,22 @@
+name: Markdown linter
+
+on:
+  pull_request:
+    types: [ "opened", "reopened", "synchronize" ]
+  push:
+    branches:
+    - '**'
+    tags-ignore:
+    - '**'
+  workflow_dispatch: {}
+
+jobs:
+  markdown-lint:
+    container:
+      image: git.cryptic.systems/volker.raschek/markdownlint:0.44.0
+    runs-on:
+    - ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4.2.2
+    - name: Lint Markdown files
+      run: markdownlint .