Use ubuntu 22.04 as the oldest ubuntu in CI

Author: kislyuk

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       max-parallel: 8
       matrix:
-        os: [ubuntu-20.04, ubuntu-latest, macos-13, macos-latest]
+        os: [ubuntu-22.04, ubuntu-latest, macos-13, macos-latest]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
     steps:
     - uses: actions/checkout@v4