add: Python 3.13 classifier to awkward-cpp (#3510)

Co-authored-by: Ianna Osborne <ianna.osborne@cern.ch>

Author: APN-Pucky

awkward-cpp/pyproject.toml

@@ -36,6 +36,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Topic :: Scientific/Engineering",
     "Topic :: Scientific/Engineering :: Information Analysis",
     "Topic :: Scientific/Engineering :: Mathematics",