Update Elixir version in CI

Author: adam12

.github/workflows/main.yml

@@ -34,10 +34,10 @@ jobs:
  ecto32:
  runs-on: ubuntu-latest
  container:
- image: elixir:1.9.1-slim
+ image: elixir:1.15.7-slim
  services:
  postgres:
- image: postgres:10.8
+ image: postgres:14
  env:
  POSTGRES_USER: postgres
  POSTGRES_PASSWORD: postgres