ci: update runner image to ubuntu-24.04

The Ubuntu 20.04 image was already removed on 2025-04-15.

Author: jelly

.github/workflows/publish.yml

@@ -5,7 +5,7 @@ on: push
 jobs:
   build-n-publish:
     name: Build and publish Python 🐍 distributions 📦 to PyPI and TestPyPI
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
 
     steps:
       - uses: actions/checkout@v4