Update workflow ubuntu image version

Previous Ubuntu version (20.4) is deprecated, switching to 22.4

Author: BlitzBanana

.github/workflows/elixir.yml

@@ -8,7 +8,7 @@ permissions:
 jobs:
   build:
     name: Build and test
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     strategy:
       matrix: