Add Python 3.11 to test matrix

Author: tomato42

.github/workflows/ci.yml

@@ -87,11 +87,10 @@ jobs:
             os: ubuntu-latest
             python-version: '3.10'
             tox-env: gmpy2py310
-          # Python 3.11a3 segfaults when running the test suite so skip it for now
-          #- name: py3.11
-          #  os: ubuntu-latest
-          #  python-version: '3.11.0-alpha.3'
-          #  tox-env: py311
+          - name: py3.11
+            os: ubuntu-latest
+            python-version: '3.11.0-beta.3'
+            tox-env: py311
           - name: pypy
             os: ubuntu-latest
             python-version: pypy-2.7