ci: remove EOL ubuntu

Author: wez

.github/workflows/linux.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, ubuntu-22.04]
+        os: [ubuntu-22.04]
     runs-on: ${{ matrix.os }}
     steps:
     - name: "checkout repo"