add testing on Python 3.11

Also update versioneer to 0.21 (with modifications to make it work with
2.6)

Author: tomato42

.github/workflows/ci.yml

@@ -82,6 +82,10 @@ jobs:
             os: ubuntu-latest
             python-version: '3.10'
             tox-env: gmpy2py310
+          - name: py3.11
+            os: ubuntu-latest
+            python-version: '3.11.0-alpha.3'
+            tox-env: py311
           - name: pypy
             os: ubuntu-latest
             python-version: pypy-2.7

src/ecdsa/__init__.py

@@ -37,13 +37,9 @@
     InvalidSharedSecretError,
 )
 from .der import UnexpectedDER
+from . import _version
 
 # This code comes from http://github.com/tlsfuzzer/python-ecdsa
-from ._version import get_versions
-
-__version__ = get_versions()["version"]
-del get_versions
-
 __all__ = [
     "curves",
     "der",
@@ -90,3 +86,5 @@
     six.b(""),
 ]
 del _hush_pyflakes
+
+__version__ = _version.get_versions()["version"]