Bump django-htmx from 1.19.0 to 1.21.0

Bumps [django-htmx](https://github.com/adamchainz/django-htmx) from 1.19.0 to 1.21.0.
- [Changelog](https://github.com/adamchainz/django-htmx/blob/main/docs/changelog.rst)
- [Commits](adamchainz/django-htmx@1.19.0...1.21.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements/requirements.txt

@@ -77,7 +77,7 @@ django-extensions==3.2.3
     #   django-anvil-consortium-manager
 django-filter==23.5
     # via django-anvil-consortium-manager
-django-htmx==1.19.0
+django-htmx==1.21.0
     # via -r requirements/requirements.in
 django-login-required-middleware==0.9.0
     # via -r requirements/requirements.in