chore(pyproject): add Python 3.10 classifier

Author: mkniewallner

pyproject.toml

@@ -24,6 +24,7 @@ classifiers = [
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3 :: Only",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",