chore(deps): update davidanson/markdownlint-cli2-action action to v20

Author: renovate[bot]

.github/workflows/markdown-lint.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v5
-      - uses: DavidAnson/markdownlint-cli2-action@v19
+      - uses: DavidAnson/markdownlint-cli2-action@v20
         if: false
         with:
           globs: 'README.md'