Bump DavidAnson/markdownlint-cli2-action from 17 to 21 (#19204)

Bumps [DavidAnson/markdownlint-cli2-action](https://github.com/davidanson/markdownlint-cli2-action) from 17 to 21.
- [Release notes](https://github.com/davidanson/markdownlint-cli2-action/releases)
- [Commits](DavidAnson/markdownlint-cli2-action@v17...v21)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/pipedream-sdk-markdown-lint.yaml

@@ -19,6 +19,6 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Lint markdown files
-        uses: DavidAnson/markdownlint-cli2-action@v17
+        uses: DavidAnson/markdownlint-cli2-action@v21
         with:
           globs: 'packages/sdk/**/*.md'