Add Elixir 1.20 to test matrix

Author: adam12

.github/workflows/main.yml

@@ -6,7 +6,7 @@ jobs:
   test:
     strategy:
       matrix:
-        elixir_version: [1.17, 1.16]
+        elixir_version: ["1.20", 1.17, 1.16]
     runs-on: ubuntu-latest
     container:
       image: elixir:${{ matrix.elixir_version }}