Bump django-bootstrap4 in /{{cookiecutter.project_slug}} (#307)

Bumps [django-bootstrap4](https://github.com/zostera/django-bootstrap4) from 21.1 to 21.2.
- [Release notes](https://github.com/zostera/django-bootstrap4/releases)
- [Changelog](https://github.com/zostera/django-bootstrap4/blob/main/CHANGELOG.md)
- [Commits](https://github.com/zostera/django-bootstrap4/commits/v21.2)

---
updated-dependencies:
- dependency-name: django-bootstrap4
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

{{cookiecutter.project_slug}}/Pipfile

@@ -18,7 +18,7 @@ psycopg2 = "<2.9"
 waitress = "~=2.0.0"
 whitenoise = "~=5.3.0"
 djangorestframework = "~=3.13.1"
-django-bootstrap4 = "~=21.1"
+django-bootstrap4 = "~=21.2"
 django-allauth = "~=0.47.0"
 django-rest-auth = "~=0.9.5"
 django-extensions = "~=3.1.5"