Bump django-multifactor from 0.5.5 to 0.6.1 in /server

Bumps [django-multifactor](https://github.com/oliwarner/django-multifactor) from 0.5.5 to 0.6.1.
- [Release notes](https://github.com/oliwarner/django-multifactor/releases)
- [Commits](https://github.com/oliwarner/django-multifactor/commits/v0.6.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

server/requirements.txt

@@ -11,7 +11,7 @@ django-decorator-include==3.0
 django-extensions==3.2.*
 django-formset-js-improved
 git+https://github.com/oliwarner/django-multifactor.git@9d08f222830d3513e88e42f68ff570d74be53948#egg=django-multifactor
-django-multifactor==0.5.5
+django-multifactor==0.6.1
 djangorestframework==3.14.*
 emoji==2.8.*
 icalendar==5.0.*