Pin ubuntu-22.04

Author: pbernet

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
       - migrate_pekko
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     env:
       # define Java options for both official sbt and sbt-extras
       JAVA_OPTS: -Xms2048M -Xmx2048M -Xss6M -XX:ReservedCodeCacheSize=256M -Dfile.encoding=UTF-8