Update Ubuntu for CI

Author: cowtowncoder

.github/workflows/main.yml

@@ -13,13 +13,12 @@ permissions:
   contents: read
 jobs:
   build:
-    runs-on: ${{ matrix.os }}
+    runs-on: 'ubuntu-22.04'
     strategy:
       fail-fast: false
       matrix:
         # Alas, JDK14 can't be yet used while build is for Java 6
         java_version: ['8', '11']
-        os: ['ubuntu-20.04']
     env:
       JAVA_OPTS: "-XX:+TieredCompilation -XX:TieredStopAtLevel=1"
     steps: