Set up test envs for Python 3.10

We should've been testing for Python 3.10 for a long time now, it's
time to start!

fixxup

.github/workflows/build-and-test.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [3.7, 3.8, 3.9]
+        python-version: ["3.7", "3.8", "3.9", "3.10"]
 
     steps:
       - uses: actions/checkout@v3

tests/docker/Dockerfile

@@ -20,6 +20,7 @@ RUN add-apt-repository ppa:deadsnakes/ppa && \
       python3.7-dbg python3.7-dev python3.7-distutils \
       python3.8-dbg python3.8-dev \
       python3.9-dbg python3.9-dev \
+      python3.10-dbg python3.10-dev \
       python3-pip
 
 RUN echo "deb http://dl.google.com/linux/chrome/deb/ stable main" > /etc/apt/sources.list.d/google-chrome.list

tox.ini

@@ -6,7 +6,10 @@
 # When changing the python or django version also change it in the tox example
 # of the documentation in hacking.rst
 [tox]
-envlist = {unit,integration,functional}-py{37,38,39}-django{32}, javascript, docs
+envlist =
+    {unit,integration,functional}-py{37,38,39,310}-django{32}
+    javascript
+    docs
 skipsdist = True
 basepython = python3.7
 
@@ -20,6 +23,7 @@ python =
     3.7: py37
     3.8: py38
     3.9: py39
+    3.10: py310
 
 [testenv]
 # Baseline test environment