chore: drop python3.6

EOL was 2021-12-23

Author: tonnico

.github/workflows/tests.yaml

@@ -23,9 +23,6 @@ jobs:
         toxenv:
           - "pep8"
         include:
-          - python-version: "3.6"
-            os: ubuntu-20.04
-            toxenv: py36
           - python-version: "3.7"
             os: ubuntu-20.04
             toxenv: py37

pyproject.toml

@@ -36,7 +36,6 @@ classifiers = [
     "Programming Language :: Python",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",
-    "Programming Language :: Python :: 3.6",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",