Drop support for Python 3.5, 3.6

Both are end-of-life (as of 2020-09-30 and 2021-12-23, respectively).

Set PyPy version to 3.7 as:
- the default version, PyPy 3.6, seems to no longer be available.
- we want to drop support for 3.6 anyway (including PyPy).
- the Python version is now required to be in `x.y` format.

Author: homeworkprod

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9, pypy3]
+        python-version: [3.7, 3.8, 3.9, pypy3.7]
 
     steps:
       # Python needs to be setup before checkout to prevent files from being

setup.py

@@ -32,8 +32,6 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 3.5',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',