Update DavidAnson/markdownlint-cli2-action action to v18

Author: renovate[bot]

.github/workflows/lint.yml

@@ -28,7 +28,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: DavidAnson/markdownlint-cli2-action@v17
+      - uses: DavidAnson/markdownlint-cli2-action@v18
         with:
           globs: |
             README.md