[pre-commit.ci] pre-commit autoupdate (#26)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -48,7 +48,7 @@ repos:
       - id: yamlfmt
         args: [--mapping, '2', --offset, '2', --sequence, '4']
   - repo: https://github.com/executablebooks/mdformat
-    rev: 0.7.19
+    rev: 0.7.21
     hooks:
       - id: mdformat
         additional_dependencies: