Announce support for Python 3.13

Change-Id: I12dbd78c723d474bb7e0048b4c2fd1a629b33647
diff --git a/pyproject.toml b/pyproject.toml
index 6487812..43bfdcd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,6 +24,7 @@
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
 ]