[deps] Update django-phonenumber-field requirement

Updates the requirements on [django-phonenumber-field](https://github.com/stefanfoulis/django-phonenumber-field) to permit the latest version.
- [Release notes](https://github.com/stefanfoulis/django-phonenumber-field/releases)
- [Changelog](https://github.com/stefanfoulis/django-phonenumber-field/blob/main/CHANGELOG.rst)
- [Commits](stefanfoulis/django-phonenumber-field@8.0.0...8.1.0)

---
updated-dependencies:
- dependency-name: django-phonenumber-field
  dependency-version: 8.1.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 django-organizations~=2.4.1
 django-extensions~=3.2.3
 django-allauth[socialaccount]~=65.6.0
-django-phonenumber-field~=8.0.0
+django-phonenumber-field~=8.1.0
 phonenumbers~=9.0.2
 openwisp-utils[rest,celery] @ https://github.com/openwisp/openwisp-utils/tarball/1.2
 packaging