ci: add Python 3.13 to the testing matrix

Author: Ljzd-PRO

.github/workflows/plugin-test.yml

@@ -27,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [ "3.9", "3.10", "3.11", "3.12" ]
+        python-version: [ "3.9", "3.10", "3.11", "3.12", "3.13" ]
     name: nonebot2 plugin test
     permissions:
       issues: read