[2.2.x] Refs #31040 -- Doc'd Python 3.9 compatibility.

Backport of e18156b6c3 from master.

docs/faq/install.txt

@@ -49,7 +49,7 @@ Django version Python versions
 1.11           2.7, 3.4, 3.5, 3.6, 3.7 (added in 1.11.17)
 2.0            3.4, 3.5, 3.6, 3.7
 2.1            3.5, 3.6, 3.7
-2.2            3.5, 3.6, 3.7, 3.8 (added in 2.2.8)
+2.2            3.5, 3.6, 3.7, 3.8 (added in 2.2.8), 3.9 (added in 2.2.17)
 ============== ===============
 
 For each version of Python, only the latest micro release (A.B.C) is officially

docs/releases/2.2.17.txt

@@ -0,0 +1,7 @@
+===========================
+Django 2.2.17 release notes
+===========================
+
+*Expected November 2, 2020*
+
+Django 2.2.17 adds compatibility with Python 3.9.

docs/releases/2.2.txt

@@ -23,9 +23,9 @@ end in April 2020.
 Python compatibility
 ====================
 
-Django 2.2 supports Python 3.5, 3.6, 3.7, and 3.8 (as of 2.2.8). We
-**highly recommend** and only officially support the latest release of each
-series.
+Django 2.2 supports Python 3.5, 3.6, 3.7, 3.8 (as of 2.2.8), and 3.9 (as of
+2.2.17). We **highly recommend** and only officially support the latest release
+of each series.
 
 .. _whats-new-2.2:
 

docs/releases/index.txt

@@ -25,6 +25,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   2.2.17
    2.2.16
    2.2.15
    2.2.14

setup.py

@@ -102,6 +102,7 @@ setup(
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3 :: Only',
         'Topic :: Internet :: WWW/HTTP',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',

tox.ini

@@ -21,7 +21,7 @@ passenv = DJANGO_SETTINGS_MODULE PYTHONPATH HOME DISPLAY
 setenv =
     PYTHONDONTWRITEBYTECODE=1
 deps =
-    py{3,35,36,37,38}: -rtests/requirements/py3.txt
+    py{3,35,36,37,38,39}: -rtests/requirements/py3.txt
     postgres: -rtests/requirements/postgres.txt
     mysql: -rtests/requirements/mysql.txt
     oracle: -rtests/requirements/oracle.txt