Add classifier for 3.11 (pymodbus-dev#1312)

Co-authored-by: jan iversen <[email protected]>

Author: alexrudd2

setup.cfg

@@ -24,6 +24,7 @@ classifiers      =
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
+    Programming Language :: Python :: 3.11
     Topic :: System :: Networking
     Topic :: Utilities
 project_urls     =