[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/DavidAnson/markdownlint-cli2: v0.20.0 → v0.21.0](DavidAnson/markdownlint-cli2@v0.20.0...v0.21.0)

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -18,7 +18,7 @@ repos:
         types_or: [c++, c]
         args: [-i, --style=file]
   - repo: https://github.com/DavidAnson/markdownlint-cli2
-    rev: v0.20.0
+    rev: v0.21.0
     hooks:
       - id: markdownlint-cli2-rules-docker
   - repo: https://github.com/codespell-project/codespell