setup.py/classifiers: specify minor python versions (tested in CI pipeline)

setup.py

@@ -32,12 +32,17 @@ setuptools.setup(
     license="GPLv3+",
     keywords=["calendar", "event", "iCal", "iCalendar", "ics", "split", "sync", "vdir"],
     classifiers=[
+        # https://pypi.org/classifiers/
         "Development Status :: 3 - Alpha",
         "Intended Audience :: End Users/Desktop",
         "Intended Audience :: System Administrators",
         "License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)",
         "Operating System :: OS Independent",
-        "Programming Language :: Python :: 3",
+        # .github/workflows/python.yml
+        "Programming Language :: Python :: 3.5",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Topic :: Utilities",
     ],
     entry_points={"console_scripts": ["ical2vdir = ical2vdir:_main",]},