TT#121955 Bump django from 3.2.14 to 3.2.15 in /requirements

Bumps [django](https://github.com/django/django) from 3.2.14 to 3.2.15.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/3.2.14...3.2.15)

Change-Id: I26c74de3db608b5ad2a9a479efd90ada85689e37

requirements/common.txt

@@ -1,5 +1,5 @@
 celery
-Django==3.2.14
+Django==3.2.15
 django-appconf
 django-assets
 django-celery-beat

t/Dockerfile

@@ -5,7 +5,7 @@ FROM docker.mgm.sipwise.com/sipwise-bullseye:latest
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2022-07-06
+ENV REFRESHED_AT 2022-08-12
 
 RUN apt-get update && apt-get install --assume-yes python3 python3-dev \
 	python3-pytest python3-pytest-pep8 \