Bump pymarkdownlnt from 0.9.20 to 0.9.21 in /{{ cookiecutter.name }} (#697)

Bumps [pymarkdownlnt](https://github.com/jackdewinter/pymarkdown) from 0.9.20 to 0.9.21.
- [Release notes](https://github.com/jackdewinter/pymarkdown/releases)
- [Changelog](https://github.com/jackdewinter/pymarkdown/blob/main/changelog.md)
- [Commits](jackdewinter/pymarkdown@v0.9.20...v0.9.21)

---
updated-dependencies:
- dependency-name: pymarkdownlnt
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

{{ cookiecutter.name }}/poetry.lock

@@ -57,7 +57,7 @@ isort = "^5.12.0"
 jedi = "^0.19.1"
 mixer = {extras = ["django"], version = "^7.2.2"}
 mypy = "^1.10.1"
-pymarkdownlnt = "^0.9.20"
+pymarkdownlnt = "^0.9.21"
 pytest-deadfixtures = "^2.2.1"
 pytest-django = "^4.7.0"
 pytest-env = "^1.1.1"