CI: Remove running on Python 3.6, setuptools is too old for PEP 660

WARNING: pytest-mqtt 0.0.0 does not provide the extra 'develop'
WARNING: pytest-mqtt 0.0.0 does not provide the extra 'test'

poe: command not found

.github/workflows/tests.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11-dev"]
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11-dev"]
       fail-fast: false
 
     env:

pyproject.toml

@@ -33,7 +33,6 @@ classifiers = [
   "Operating System :: POSIX :: Linux",
   "Operating System :: Unix",
   "Programming Language :: Python",
-  "Programming Language :: Python :: 3.6",
   "Programming Language :: Python :: 3.7",
   "Programming Language :: Python :: 3.8",
   "Programming Language :: Python :: 3.9",