Use ubuntu-latest

Ubuntu 20.04 was retired 2025-04-15

This follows the same thing we did in puppetlabs/phoenix-github-actions@36a826a

Author: joshcooper

.github/workflows/checks.yaml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   rubocop_checks:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: RuboCop
     steps:
       - name: Checkout current PR

.github/workflows/unit_tests.yaml

@@ -24,7 +24,9 @@ jobs:
           - '3.2'
           - 'jruby-9.3.14.0'
           - 'jruby-9.4.8.0'
-    runs-on: ubuntu-20.04
+    # 24.04 doesn't support older jruby versions, so use 22.04 as middle ground
+    # When we drop testing against puppet7, then we can use newer ubuntu.
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout current PR
         uses: actions/checkout@v4