build(deps): bump DavidAnson/markdownlint-cli2-action from 20 to 21

Bumps [DavidAnson/markdownlint-cli2-action](https://github.com/davidanson/markdownlint-cli2-action) from 20 to 21.
- [Release notes](https://github.com/davidanson/markdownlint-cli2-action/releases)
- [Commits](DavidAnson/markdownlint-cli2-action@v20...v21)

---
updated-dependencies:
- dependency-name: DavidAnson/markdownlint-cli2-action
  dependency-version: '21'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/lints.yml

@@ -13,7 +13,7 @@ jobs:
         runs-on: ubuntu-latest
         steps:
         - uses: actions/checkout@v6
-        - uses: DavidAnson/markdownlint-cli2-action@v20
+        - uses: DavidAnson/markdownlint-cli2-action@v21
           with:
             fix: true
             globs: |