Note support for Python 3.9 (#8665)

As expected, all tests pass locally without modification.

Signed-off-by: Dan Callahan <danc@element.io>

INSTALL.md

@@ -57,7 +57,7 @@ light workloads.
 System requirements:
 
 - POSIX-compliant system (tested on Linux & OS X)
-- Python 3.5.2 or later, up to Python 3.8.
+- Python 3.5.2 or later, up to Python 3.9.
 - At least 1GB of free RAM if you want to join large public rooms like #matrix:matrix.org
 
 Synapse is written in Python but some of the libraries it uses are written in

changelog.d/8665.doc

@@ -0,0 +1 @@
+Note support for Python 3.9.

setup.py

@@ -131,6 +131,7 @@ setup(
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
     ],
     scripts=["synctl"] + glob.glob("scripts/*"),
     cmdclass={"test": TestCommand},

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = packaging, py35, py36, py37, py38, check_codestyle, check_isort
+envlist = packaging, py35, py36, py37, py38, py39, check_codestyle, check_isort
 
 [base]
 extras = test