Remove Ubuntu 18.04 from test matrix

Author: kislyuk

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       max-parallel: 8
       matrix:
-        os: [ubuntu-18.04, ubuntu-22.04]
+        os: [ubuntu-20.04, ubuntu-24.04]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
     steps:
     - uses: actions/checkout@v4