Enable testing with Python 3.11

We should add Python 3.11 to our testing matrix in order to antecipate possible problems (even if we don't attempt to solve any of them right away).

.github/workflows/main.yml

@@ -37,6 +37,7 @@ jobs:
           "windows-py38",
           "windows-py39",
           "windows-py310",
+          "windows-py311",
 
           "ubuntu-py37",
           "ubuntu-py37-pluggy",
@@ -44,6 +45,7 @@ jobs:
           "ubuntu-py38",
           "ubuntu-py39",
           "ubuntu-py310",
+          "ubuntu-py311",
           "ubuntu-pypy3",
 
           "macos-py37",
@@ -78,6 +80,10 @@ jobs:
             python: "3.10"
             os: windows-latest
             tox_env: "py310-xdist"
+          - name: "windows-py311"
+            python: "3.11.0-alpha.3"
+            os: windows-latest
+            tox_env: "py311"
 
           - name: "ubuntu-py37"
             python: "3.7"
@@ -104,6 +110,10 @@ jobs:
             python: "3.10"
             os: ubuntu-latest
             tox_env: "py310-xdist"
+          - name: "ubuntu-py311"
+            python: "3.11.0-alpha.3"
+            os: ubuntu-latest
+            tox_env: "py311"
           - name: "ubuntu-pypy3"
             python: "pypy-3.7"
             os: ubuntu-latest

tox.ini

@@ -8,6 +8,7 @@ envlist =
     py38
     py39
     py310
+    py311
     pypy3
     py37-{pexpect,xdist,unittestextras,numpy,pluggymain}
     doctesting