pinned the ubuntu version in the Test action, to ensure support for jruby 9.4.0.0 (#1518)

Author: jar-stripe

.github/workflows/ci.yml

@@ -40,7 +40,8 @@ jobs:
 
   test:
     name: Test (${{ matrix.ruby-version }})
-    runs-on: ubuntu-latest
+    # this is needed because our JRuby test version isnt supported on ubuntu-24 (which is now ubuntu-latest)
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         ruby-version: [2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, '3.3', jruby-9.4.0.0, truffleruby-head]