ci: bump Ubuntu version for UnusedMissingReturn jobs

Author: bonzini

.github/workflows/unusedargs_missingreturn.yml

@@ -42,7 +42,7 @@ permissions:
 jobs:
 
   linux:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5